If you have experienced even a few minutes of cable news coverage or handful of newspaper op-eds on American foreign policy, there is a word you will have encountered over and over again: credibility.

The United States, according to this theory, has to follow through on every threat and confront every adversary in order to maintain America’s global credibility. If it fails to stand up to challengers in one place, then they will rise up everywhere, and America will see its global standing, and thus its power in the world, crumble.

This argument has dominated Washington especially in the three years since President Barack Obama declined to bomb Syrian leader Bashar al-Assad as punishment for using chemical weapons. Proponents of “credibility” say this matters for more than just Syria.

American allies came to distrust and drift away from US leadership, they argued. And American adversaries grew emboldened — including Russia’s Vladimir Putin, whose subsequent invasion of Ukraine was said to be a direct result of weakened American credibility.

“Putin believes Obama does not have the intestinal fortitude to stand up to him in Ukraine. He thinks Obama will talk tough and then look for a way out — just like he did with Assad,” wrote Washington Post columnist Marc Thiessen.

“Syria has become the graveyard of U.S. credibility,” columnist Michael Gerson wrote in the same paper.

This theory is not exclusive to overheated op-eds. It is pervasive, almost to the point of consensus, in much of Washington’s foreign policy community, including among many policy-makers — and has been that way longer than perhaps even proponents realize.

In 1950, as the United States considered whether or not to intervene in the Korean War, a CIA report urged the US to intervene so as to uphold its credibility far away in Europe:

A failure to draw the line would have seriously discredited the whole US policy of containment, gravely handicapping US efforts to maintain alliances and build political influence with the Western European powers and with other nations closely aligned with the US.

Secretary of State Dean Acheson agreed, fearing that European leaders would be in a “near-panic, as they watched to see whether the United States would act.” If the US did not invade Korea, Acheson worried, Europe’s frail post-war order could be at risk.

And this is not just an American belief. As former National Security Council official Philip Gordon recounted recently, France kept fighting in Algeria, long after the costly war appeared lost, partly out of fear of losing credibility.

“The credibility issue—if you pull out of Algeria, boy, you lose face, right? And so the argument was, stay in and keep a lid on it,” Gordon told the Atlantic’s Jeffrey Goldberg.

But there is a problem with this theory of credibility: It does not appear to be real. Political scientists have investigated this theory over and over, and have repeatedly disproven it.

Yet the belief in credibility persists, dominating America’s foreign policy debate, steering the United States toward military action abroad in pursuit of a strategic asset — the credibility of America’s reputation — that turns out not to exist.

How did this idea become so entrenched in Washington, and why does it persist despite being repeatedly debunked? What does it mean to have so many of America’s foreign policy discussions turn around an idea that is demonstrably false — and what can this tell us about how and why America intervenes abroad?

The credibility myth

When Americans talk about “credibility” in foreign policy, what they are usually describing is something that political scientists instead call reputational or reputation-based credibility.

In political science, “credibility” usually refers to specific promises or threats, and in this case the research does say that credibility is real. For example, if the US pledges to defend South Korea from a North Korean invasion, then it matters that the US convince both Koreas that this pledge is credible, for example by stationing US troops in South Korea.

That is the formal definition of credibility in foreign policy, it’s real, and it matters. But when “credibility” is used colloquially, it typically refers to a very different kind of credibility, one based entirely in a country’s or leader’s reputation from its actions in other disputes or conflicts. (This article uses the colloquial definition of credibility, except where noted otherwise.)

Under this line of thinking, if the US fails to follow through on a threat or stand up to a challenger in one part of the world, then its allies and enemies globally will be more likely to conclude that all American threats are empty, and that America can be pushed around. If the US backed down once, it will back down again.

It’s easy to see how people could be attracted to this idea, which puts complicated geo-politics in simple and familiar human terms. It encourages us to think of states as just like people.

But states are not people, and this theory, for all its appealing simplicity, is not correct. There is no evidence that America’s allies or enemies change their behavior based on conclusions about America’s reputation for credibility, or that such a form of reputation even exists in foreign policy.

“Do leaders assume that other leaders who have been irresolute in the past will be irresolute in the future and that, therefore, their threats are not credible?” the University of Washington’s Jonathan Mercer wrote, in introducing his research on this question.

“No; broad and deep evidence dispels that notion,” Mercer concluded. “As the record shows, reputations do not matter.”

A 1984 Yale University study, for example, examined dozens of cases from 1900 to 1980 to look for signs that, if a country stood down in one confrontation, it would face more challengers elsewhere. The answer was no: “deterrence success is not systematically associated … with the defender’s firmness or lack of it in previous crises.”

Historians have also looked at specific incidents where the US thought its credibility was on the line and determined that we were simply mistaken.

Acheson’s warning that the US had to invade Korea to reassure its European allies, for example, turned out to be wrong: British and French officials in fact worried the Americans were going to pull them into a far-away war.

During the Vietnam War, American officials could see that they were losing, but for years worried that withdrawing would communicate weakness to the Soviet Union, emboldening Moscow to test American commitments elsewhere. Even if Vietnam was lost, American credibility had to be defended.

As historian Ted Hopf has shown, the Americans could not have had it more wrong: Soviet leaders never reached any such conclusion, and in fact were puzzled as to why the US sacrificed so many lives for a war that was clearly lost.

If that’s not enough evidence for you, try considering reputational credibility from the opposite point of view, and it starts to look more obviously ridiculous. Dartmouth’s Daryl Press once pointed out to my colleague Dylan Matthews that Soviet premier Nikita Khrushchev repeatedly threatened to eject the American-led forces occupying West Berlin, but he backed down. The US didn’t consider him one iota less “credible” for this, and during the following year’s Cuban Missile Crisis took his threats very seriously.

The idea of reputational credibility has also been debunked in the most well-known recent case: the notion that America’s failure to bomb Syria in 2013 emboldened Russian President Vladimir Putin.

Proponents of reputational credibility took Putin’s 2014 Ukraine invasions as vindication. Surely Putin only invaded because America had damaged its credibility in Syria, they argued. In their view, it showed why it is so crucial for the US to maintain its reputational credibility by never backing down from military interventions.

Julia Ioffe recently investigated this theory for the Atlantic, asking foreign policy officials and experts in Moscow whether there was merit to it. She seemed to reach the same conclusion as have many Russia analysts: that Putin invaded Ukraine for reasons specific to Ukraine. America’s supposed reputation loss in Syria appeared to play no role. Some of Ioffe’s sources seemed to not even understand the argument of how Syria and Ukraine would connect.

The credibility trap

You will notice something these incidents have in common. In every case, a belief in “credibility” pulls the United States toward fighting a war for the wrong reasons, or toward staying in a war longer than is worthwhile.

This mistaken belief has repeatedly helped to drive American military action abroad, Dartmouth’s Jennifer Lind demonstrates in a new article in International Security Studies Forum.

“Indeed, from Korea, to Vietnam, to Bosnia, to Libya, to President Barack Obama’s ‘red line’ in Syria, debates about U.S. intervention are thick with admonitions that ‘Our Credibility Is On The Line,'” Lind writes.

The logic of reputational credibility can only ever lead to the same conclusion: toward the use of American military force abroad, even in cases where there is no clear reason to intervene and where the downsides of intervention would seem to outweigh the upsides. It is a compass that only points in one direction.

In this theory, the use of force is inherently good, regardless of how or where the bombs fall, because it strengthens American leadership globally. And an absence of American military action is almost always bad, because it is said to invite new problems and greater threats.

“Every time analysts and leaders call for war, they warn that inaction will jeopardize America’s credibility,” Lind and Press, her husband, have previously written in Foreign Policy.

Alarmingly, despite the mounting evidence against reputation theory, it continues to drive US foreign policy discourse — and has recently even been integrated into the formal legal basis of American foreign policy.

“Credibility has migrated from foreign policy into the constitutional law of war powers,” Vanderbilt’s Ganesh Sitaraman found in a 2014 Harvard Law Review article:

In a series of opinions, including on Somalia (1992), Haiti (2004), and Libya (2011), the Justice Department’s Office of Legal Counsel (OLC) has argued that the credibility of the United Nations Security Council is a “national interest” that can justify presidential authority to use military force without prior congressional authorization.

The 2011 case is particularly striking, given that it occurred under President Obama, who has personally denounced reputational credibility as “so easily disposed of that I’m always puzzled by how people make the argument.”

Yet reputation theory is so prevalent in American thinking that even a president who specifically opposes that theory — and is himself a constitutional lawyer — has allowed it to be formally integrating into his government’s legal case for war.

Are America’s allies to blame? Or are we?

If reputational credibility has been so repeatedly debunked, both in specific instances and as a theory, why does it continue to loom so large in America’s foreign policy discourse?

Tufts University’s Michael Beckley hinted at one possible explanation in a much-discussed article last year in International Security: Could it have something to do with America’s uniquely broad network of alliances?

Beckley’s article was actually asking a different question — whether those alliances lead the US to war, by allowing allies to “entangle” it in foreign conflict. (Beckley concludes the answer is no; other scholars have disputed his findings.)

But, in reviewing so-called “entanglement theory,” Beckley points out that reputational credibility, even if it doesn’t exist in the world, is something that definitely exists in the minds of foreign leaders and foreign policy decision-makers.

“The alliance comes to be perceived as an end in itself, transcending the more concrete national security interests for which it was initially conceived,” political scientist Jack Levy wrote in a well-known 1981 paper (which Beckley cites). Here’s the key quote:

Political decision makers come to believe that support for one’s allies, regardless of its consequences, is essential for their national prestige, and that the failure to provide support would ultimately result in their diplomatic isolation in a hostile and threatening world.

So it’s not that reputation is a real thing that compels states to act in a certain way, but rather that individual decision-makers are driven by their own mistaken belief in reputation. As a result, Beckley writes, “reputational concerns can drive states into wars over trivial interests in peripheral places.”

Some scholars, including Levy, argue that America’s allies promote the idea of reputation, as a means to convince the United States to commit more resources to serve their own interests.

Foreign leaders do seem to become awfully preoccupied with American credibility when they want the US to take military action on their behalf. When the US failed to bomb Syria in 2013, for example, Syria’s enemies in the region — Arab leaders who are also allied with the US — declared that American credibility was at stake.

“I think I believe in American power more than Obama does,” Jordan’s King Abdullah II said of Obama’s decision to not bomb Syria.

This comes at a time when the US has grown unusually indulgent of its allies, as Jeremy Shapiro and Richard Sokolsky argue in a recent article. This has made American policymakers more likely to heed allies’ demands and take their claims at face value.

But Dartmouth’s Jennifer Lind finds evidence that allies make this argument only opportunistically, and almost always about conflicts in which they are directly involved. They might speak in the language of reputation theory, but their behavior suggests that they do not really believe in it.

Reputation theory, after all, says that America’s allies would want the US to intervene as much as possible in other conflicts, when in fact the opposite is usually true.

In fact, so-called reputation is actually driven almost entirely by internal American dynamics. Consider America’s belief that it had to intervene in Korea to reassure European allies, who in fact wanted no such thing.

Lind makes this point well by citing America’s pledge to defend Taiwan from a possible Chinese invasion. According to reputation theory, Asian leaders who also fear Chinese aggression would want the US to make and uphold this pledge. American policymakers indeed believe this, and it is one reason (albeit far from the only reason) why the US has pledged to fight in such a war.

“Many U.S. leaders and foreign policy elites today argue that, in the event of a war in the Taiwan strait, the United States must defend Taiwan or see its credibility collapse,” Lind writes.

In reality, the opposite is true. American allies in Asia, Lind writes, “make it clear that they under no circumstances want war in the Taiwan strait, and fear that the Americans will someday fight one with China.”

The Taiwan example is instructive, if alarming: America’s foreign policy community believes something that is flatly untrue. And while a Sino-American war over Taiwan is extremely unlikely, it looked substantially less unlikely in the 1990s. It is concerning that American policymakers were committing the US to fight such a war in part because they believed something that was 180-degrees the opposite of reality.

The point is not just that America’s mistaken belief in credibility is dangerous, but also that it does not come from allies. It comes from us.

Credibility mythology: America’s go-to case for war

So what is really going on? Why are America’s foreign policy leaders and thinker so set on believing something that has been repeatedly demonstrated as untrue?

Political scientists prefer to answer questions that are falsifiable — is credibility real? — than to pathologize policymakers who choose to believe and act upon a wrong theory.

But people who’ve researched this theory suggest it has two likely draws. First, it is a reliable and effective argument for publicly selling military action. And, second, the notion of “credibility” tells a story that can be very appealing to American foreign policy elites, leading them to want to believe something they should know to question.

It’s easy to overstate the degree to which this phenomenon is driven by the first of those two factors, the idea that credibility theory can be politically useful for selling military action. But it really can be.

Because the logic of reputation-based credibility always points toward taking military action, and because unlike most foreign policy precepts it is very intuitive and easy to understand, foreign policy elites who want some sort of military action have a strong incentive to make that argument.

“The credibility argument is simply an easy (and hard to disprove) way for elites to sell the foreign policy they’re most interested in to the American people, whether that’s domino theory, primacy, or intervention in some conflict,” Emma Ashford of the Cato Institute pointed out.

“Credibility is an intuitive and hard to refute argument, even if larger studies show it to be false,” she added.

Policymakers or foreign leaders who might have several reasons to seek some specific military action, even if some of those reasons are good, will be inclined to emphasize “credibility” arguments because they are easier to sell.

As a result, every time there is a debate over possible military action, the airwaves fill with warnings about American credibility.

Studies have shown that many Americans still believe that Obamacare includes “death panels,” despite that myth being both frequently refuted and on-its-face ridiculous. Imagine how pervasive that myth would be if its wrongness were less obvious, if both Democrats and Republicans repeated it, as they do with credibility, and if rebuttals appeared only in obscure political science journals. It would be everywhere.

America’s foreign policy debate, after all, doesn’t exactly play out in the pages of International Security Studies. It plays out in mass-market media: on cable news and in newspaper op-ed pages, mediums that privilege short, simple, intuitive arguments.

What could be simpler and more intuitive than telling people that countries are just like people, that we have to stand up to this bully or we’ll get our lunch money taken again?

Credibility mythology: the stories we tell ourselves about American power

But this does not explain why so many policymakers seem to earnestly believe the theory. And they really do. You hear it repeated on think tank panels, at off-the-record roundtables, even in informal conversations with policymakers.

The idea of American credibility, I have noticed, can evoke something like an emotional reaction in many Washington foreign policy figures. It can seem to be a core belief, less in the manner of a political science axiom, and more in the way that, say, being “pro-Israel” is a core belief, or that America’s responsibility to uphold human rights abroad is a core belief.

American foreign policy is ultimately made by human beings, not by emotionless automatons. And like any other industry, the people who work in it tend to privilege a worldview in which their work is important and positive. But that can mean seeing American foreign policy itself as important and positive, maybe more so than it always is.

We understand intuitively how this happens in other industries: why a technology executive would overstate the world-changing power of smartphone apps, or would personalize Silicon Valley as an extension of their personal values. It should not be shocking that American foreign policy professionals — a relatively small and insular community — would indulge this very human habit as well.

And that gets to the second, and perhaps core, driver of this mistaken belief: reputational credibility asserts a vision of the world and America that can be very appealing, on both professional and personal terms, to American foreign policy professionals.

It portrays the world as a place where the world turns on American power, whose assertion is inherently a force for justice and stability.

It’s a world where the United States is the protagonist of every story — because every conflict is a test of our credibility, we are at the center even of events that seem to have nothing to do with us — and where the US is best served by personifying the characteristics of a Hollywood action movie hero.

Left, Secretary of State Dean Acheson, who believed the US should intervene in Korea in part to reassure allies such as Britain’s Winston Churchill of American credibility. Right, an American marine uses a flamethrower in Korea. (Getty)

The world’s default state, in this telling, is peaceful American hegemony, where every foreign leader is restrained from any bad action anywhere by their belief in American-enforced justice. If problems arise, it is only because the world has drifted from this default, which can be restored by reasserting American credibility.

American foreign policy professionals, in this view, can feel uncomplicated pride and certainty about America’s — and thus their own — role in the world.

The military historian Andrew Bacevich has observed these sorts of mythical and self-actualizing beliefs in American power in the United States’ repeated interventions in the Middle East, he writes in a new book.

American policymakers often decided to launch these wars, he found, based on “destructive myths about the efficacy of American military power” and “a presumption that using military power signified to friends and foes that Washington was getting serious about a problem,” the journalist David Rohde writes in a review.

Robert Farley, a University of Kentucky scholar who writes frequently on this issue, offered a version of this theory that looks different only on first glance.

“I actually sat down last night with Jon Mercer (one of the bigger voices in the anti-reputation set), and we struggled to figure this one out,” Farley told me in an email. (His is the same Mercer quoted elsewhere in this article.)

“The normal answers — Munich analogy, Cold War rational deterrence thought, American political culture — don’t really serve as very useful explanations,” he said, because there is evidence that European states prior to World War I also acted on misguided notions of reputation-based credibility.

“If I had to, I’d probably say that it’s gendered,” he suggested, which sounded silly to me until I considered his argument.

“The toughness fascination emerges from a variety of gender tropes that extend back pretty far that associate toughness with manliness,” he wrote. “This understanding manifests in diplomacy through the obsession with reputation. Combine that with the regular diplomatic over-emphasis on the effect of US action, and you get a compulsion to look at every event in terms of whose dick is longer.”

While gendered norms do not necessarily have to play out along black-and-white gender lines, it is hard to ignore that American foreign policy is notoriously male-dominated. Proponents of reputation theory tend to speak in explicitly male metaphors — playground brawls, barroom fights, sports matches — whereas critics of reputation are often women. That seems striking.

I admit I am most persuaded, though, by Bacevich’s suggestion that American foreign policy professionals, regardless of gender, have been drawn to myths of American credibility that allow them to see their work, and to some extent themselves, in a more flattering and uncomplicated light.

You can see evidence of these myths when you look at the nature of the gap between reality and perception on credibility.

The reality, we know from the research, is that American action in one place, let’s say Syria, does not have any reputation-based implications for other places, such as Ukraine. Nor is it the case that other countries, such as Russia, change their behavior based on their perception of America’s reputation.

But the perception is that America is so uniquely important that allies and adversaries alike make important decisions based less on their national interests and more on simply how they feel about America and the American president.

While this might look like we are putting allies’ interests before our own, in fact we are asserting a vision of ourselves in which we are more important to those countries — and to the world — than we actually are.

Russia’s invasion of Ukraine is not about Ukrainian factors or Russian interests, in our view, but rather it is a story about America failing to live up to its ideals in the world.

Rather than admit that some things are beyond our control, reputation theory allows us to believe that we can prevent bad things from happening in the world simply by being truer to ourselves. It is an appealing message. Unfortunately, the world simply doesn’t work that way.

When Ashton Carter began his career at the Pentagon, in 1993, geopolitics was changing more rapidly than it had at any point since the Second World War. As the Cold War ended, a new world was taking its place, one dominated by American power.

Carter, at the time, expected that America’s greatest challenge in that world — and, by extension, the focus of his own career — would be limiting the spread of nuclear weapons, he told me in a recent interview at the Pentagon. And the greatest threat, he thought, would be political instability within nuclear-armed Russia.

“That was the riveting challenge of that time. We look back now, and I remember how fearful that was,” he said. “But it worked out extraordinarily well.”

Twenty-some years later, Carter now runs the Pentagon as defense secretary. The world, and the challenges it presents for the United States, turned out somewhat differently than he, or anyone else, had expected.

What Carter has seen over the past two decades, and has often overseen, is the long and difficult process whereby the United States has tried, and at times struggled, to navigate those unexpected turns in the grand experiment that is the post–Cold War world.

The challenges of this era have only recently become clear: the failure and collapse of weak states, which can bring terrorism, civil war, and refugee influxes; rogue states that resist the American-led order and proliferate dangerous weapons; and now, according to Carter, a return to “great power competition.”

In a lengthy and wide-ranging conversation, Carter expounded at length on those challenges: how they’ve changed, what the US has learned in its successes and stumbles with them, and what he sees coming. You can read the interview in full here.

But I was struck, in our conversation, by the frequency with which Carter framed today’s world within those same dynamics that had preoccupied his early career: great power rivalries, nuclear weapons, and the power of deterrence to keep the world in line.

It’s not that he’s unconcerned with terrorism or rogue states, both of which he discussed at length. But he clearly drew from his experiences in the 1980s and ’90s an acute sensitivity to the world-shaking stakes of great power rivalries, and a firm belief in the role that deterrence and nuclear weapons still play.

Carter described a world where not just American power but also global peace and stability will be increasingly challenged by other powers. He returned over and over to the same answer to this problem: the power of deterrence, backed up by overwhelming American superiority and, ultimately, by nuclear weapons.

But deterrence works on decades-old understandings of warfare that are, today, rapidly changing. As countries develop new tools and techniques of war, Carter warned that deterrence, the foundation on which American power and global stability are built, needs to change as well.

That is not a challenge that grabs as many headlines as terrorism or rogue states. But the stakes — the international order as know it, 70 years of peace between the major powers, and the thousands of nuclear warheads backing it up — could not be higher.

A changing world

In an institution as vast and expensive as the American military, budget and strategy can often be synonyms. And Carter, in writing and selling the final Pentagon budget of the Obama era, has said he is trying to prepare the United States for “a return to great power competition.”

That is a world, he has said, in which Russia and China, while still not America’s military equals, can nonetheless challenge the American-led post–Cold War order. It’s a problem “we haven’t had to worry about … for 25 years” but that is becoming increasingly real in Europe and in the Pacific.

I asked Carter why he believed this was happening — what is driving the problem, and thus, by extension, what is the appropriate response?

In answering, he characterized Russia and China as driven not by cold, hard power politics — which would thus suggest the US could negotiate a mutually beneficial resolution to any disagreement — but rather by the ideologies of their governments.

Vladimir Putin’s Russia, he suggested, is “trying to justify itself to its people on how much it can stand against the West.” This has led it to “emphasize military confrontation with the West, anti-Western propaganda, and especially the nuclear dimension of that.”

As for China, he described that country’s recent military expansionism as less cynical than Russia’s, instead rooted in historical grievances and suspicion of American power.

While Carter insisted the US has no problem with China’s power growing commensurate to its economy, he suggested that the country is also driven by “the idea [in China] that we need to right the wrongs of the past and dominate our region, and reject the system of rules-based order that we associate with the United States.”

While the American-led order serves China, he argued, “There’s a part of the Chinese mind that thinks that’s an American creation, rather than a good in itself.”

“In China, it’s a feeling of destiny about dominating a region rather than participating in a region,” he went on.

While Carter was careful not to call the Chinese leadership irrational, he clearly sees Beijing as acting against its own interests. He had hoped, he said, that “the logic of the situation would ultimately prevail over the emotion of history.” Until it does, “we have to understand that China is building up its military, it’s trying to intimidate many of its neighbors.”

In response to Russian and Chinese actions, he said, “I am making investments in high-end capabilities of a kind we might not have thought 10 years ago we’d need to make. We’re trying to catch up in some areas, advanced technology areas, with respect to China.”

This is a somewhat different attitude from what you hear in, say, the State Department, where many policymakers share Carter’s criticisms of Beijing and Moscow but believe the US should respond with greater engagement, using sticks and carrots to encourage cooperation and discourage what they see as bad behavior.

Carter seems to take a harder line, seeking primarily to deter Russia and China rather than negotiate with them.

“Negotiating with other great powers about how we can together help the world progress to mutual benefit, all of that is fine,” he said. “But if you have the attitude that you’re aggrieved, and pressing your grievance rather than negotiating the future is what it’s about, that makes it very difficult for us.”

I suspect this is less a function of Carter’s personal views than it is of the Pentagon’s traditional role in US foreign policy, which has been one of upholding and defending the international order against other powers — an approach that is more zero-sum.

US and Philippines forces conduct exercises near the South China Sea. (TED ALJIBE/AFP/Getty)

There is a long-held worldview in the US military that sees American military dominance as providing stability, and this stability as enabling much of the peace and prosperity of the postwar era. In that view, any challenge to American dominance is a challenge to global peace and prosperity itself.

“What’s kept the peace in that region all those many decades,” Carter said of Asia-Pacific, “was the system of rules-based order and the pivotal role of the American military in the region.”

Carter also seems to see renewed great power competition as a dynamic that China and Russia have forced onto the US — meaning, in his view, that it is on them to end it.

When I pointed out that Moscow and Beijing see themselves as merely seeking a larger role in the world commensurate to their growing power, he responded, “In Vladimir Putin’s Russia, you have a deliberate tinge of thwarting America as an end in itself, not a, ‘Hey, look, we need to sit down together and accommodate one another.'”

Unlike Secretary of State John Kerry, who often meets and appears publicly with Russian Foreign Minister Sergei Lavrov, it is difficult to imagine Carter doing lots of glad-handing with his Russian counterpart.

The fog of hybrid and cyber war

If the problem is renewed great power competition, then Carter’s solution is an updated version of the strategy that saw the US through the Cold War: deterrence.

Under deterrence theory, countries give one another clear warnings about what actions will trigger a retaliation. And they make sure those warnings are backed up by overwhelming military force, such that no country would dare cross another’s red lines.

A classic example is Cold War–era Berlin: The US and its allies made clear that if the Soviet Union invaded West Berlin, they would declare war. In this way, countries can protect their vital interests — in this case, a free West Berlin — while also preventing the outbreak of war.

Deterrence is why the Cold War stayed cold, and it’s why the world’s major powers have not fought a war with one another since 1945. It still applies today, but as the technology and norms of warfare are changing, Carter says deterrence needs to change as well.

“As we get into new domains, like cyber and space, and we try to situate old and very solid ideas like deterrence in those new domains, it requires some thought,” he said. “In the case of space, for example, we’re still developing those understandings.”

A Ukrainian soldier stands watch near the front lines with pro-Russian separatist rebels. (MANU BRABO/AFP/Getty)

This was an idea he mentioned several times in our conversation: updating deterrence to apply to a changing world. And one of the most urgent changes has been Russia’s development of new, asymmetric techniques sometimes called hybrid war.

“We’re reinvigorating NATO with a new playbook, different from [that of] the Cold War, to deal with, for example, the little green men phenomena that you saw in Ukraine,” Carter said, referring to the unmarked Russian special forces that seized Crimea in 2014.

Deterrence, after all, is an idea from a different era, when “war” meant tanks rolling across borders, armies invading cities. And deterrence works on certainty: Certainty about who is doing what, and what actions will spark retaliation.

Hybrid war is all about creating uncertainty: special forces dressed up as vigilantes, attacks meant to create chaos more than seize territory, propaganda and misinformation meant to spark panic or popular unrest.

These sorts of attacks are deniable — how do you threaten to retaliate against an attack if you can’t prove who launched it? And they exist outside the norms of what we do and do not consider war, potentially allowing states like Russia to subvert norms of deterrence.

When I asked Carter about this, he answered that deterrence had to be about more than just coldly calculated red lines and retaliatory threats. It also needs to have a kind of psychological effect, and thereby compensate for any uncertainty created by line-blurring methods such as hybrid war.

“It has the word ‘terror’ inside it, right? ‘Deterrence,'” he said. “That’s what it’s about, is you scare someone away from doing something you don’t want them to do by making them fear the consequences.”

In other words, even if countries like Russia can use new tools such as hybrid warfare to blur or inch across the traditional lines of deterrence, then the US should make sure that the stakes of getting caught are sufficiently high to deter them from doing so.

“If you’re attacking American interests, there will be a response,” he elaborated later in the conversation. “It’s important to communicate that fact, that you’re prepared for it, we know exactly what we’re going to do, and you will regret the consequences of your act and you should be fearful of those consequences and thus not do it in the first place.”

This problem is especially acute with regards to cyber war. As defense analysts increasingly warn, the world has not yet established clear norms for cyber conflict.

When does a state-sponsored hack become an act of war? Is it when the hackers steal military secrets? When they attack military communications? What about if they cause physical damage, as Iranian state-sponsored hackers could have done, but did not, when they accessed the controls for a dam in New York state?

The world has not yet established clear, agreed-upon answers to these questions. This makes it harder for the US to effectively deter cyber attacks because it has trouble articulating what will draw a response, and what sort of response.

Carter acknowledged that these norms are still being established. But he again argued that overwhelming US military superiority would deter even the sorts of attacks, such as cyber, to which deterrence has not traditionally applied.

“If you attack us in cyberspace, it’s an attack,” he said, as if speaking to a hypothetical adversary. “I’m very straightforward. An attack is an attack. We won’t necessarily respond in space, or respond in cyber, we may respond in some other way, but we will respond and you need to understand that.”

Carter also nodded to a risk that many in NATO have been warning about since 2014: that some Russian provocation, calculated to blur lines of deterrence without crossing them, could overreach, unintentionally crossing those lines by accident or miscalculation, blundering Europe into an unwanted conflict.

“You can’t stop a conflict that your enemy deliberately provokes, but you can try to prevent ones they blunder into by underestimating you,” he said. “One of the ways you do that is by signaling clearly and having dialogue.”

The way to reduce this risk, in his view, is for the US military to regularly communicate with the Russian and Chinese militaries, so as to prevent any misperception and control any incident from spiraling out of control.

But when I asked Carter if he was satisfied with the level of military-to-military cooperation, he answered flatly, “No.”

“I’d like to see more in general, but it takes two to tango,” he said. “It’s not just the amount; it’s the character of the dialogue and the willingness of those parties to have a dialogue of a kind that we would regard as fruitful. That’s not everything that it should be.”

“The single most fearsome and dangerous technology created by humankind”

Any conversation about deterrence or modern great power rivalry will inevitably turn to the piece of technology that has been at the heart of major power dynamics since the 1950s: nuclear weapons.

Their terrible power, after all, is what makes deterrence so effective — who would risk a war that could literally end the world? — but also so dangerous.

To make the nuclear deterrent credible, we have dotted the globe with air-, land-, and sea-based warheads, ready within a few minutes’ notice to target the world’s major cities — a threat to kill millions made credible enough that, we hope, it never has to be carried out.

A deactivated Titan II nuclear missile silo in Arizona. (BRENDAN SMIALOWSKI/AFP/Getty)

Carter, who has worked on nuclear weapons for decades, is intimately familiar with their power and with the intricate theories that have led us to build 7,100 warheads and deploy more than 1,500.

But I asked him to consider a story of someone confronting the logic of nuclear deterrence for the first time.

In 1989, President George H.W. Bush appointed a Wyoming Congress member named Dick Cheney as secretary of defense. New to the role, Cheney traveled to Nebraska, where US Strategic Command is based, to familiarize himself with the body that oversees, among other things, America’s nuclear weapons.

Amid what were surely several long days of dry policy briefings, Cheney was shown a video on an esoteric technical issue that nuclear policy wonks call fratricide.

In a nuclear launch, you have to time your strikes carefully. Otherwise, as nuclear expert Jeffrey Lewis wrote in a column recounting the incident, “the blast, electromagnetic pulse, and debris from the first wave of nuclear weapons in an attack will damage subsequent waves.”

Whoever was briefing Cheney decided the best way to explain fratricide was by showing him the US nuclear strike plans for part of Moscow. The video illustrated each strike with a red dot. As the scene stretched on, one dot after another appeared, blanketing one of the world’s most populous cities. It indicated 69 nuclear strikes on the suburb of Pushkino alone.

As Cheney saw America’s nuclear war plans unfold before his eyes, he reacted the way that anybody would: with horror.

“Moscow turned slowly into a solid red, covered over and over with ludicrous targets,” a participant at the meeting recounted to the scholar Janne Nolan. “Cheney started squirming around and finally asked one of his military aides why we were doing this kind of thing.”

Surely Carter had seen people express this reaction many times in his career, I pointed out.

“I do, I hear it all the time,” he answered. “You never get quite used to how terrible such a situation would be.”

I expected Carter to downplay the threat of nuclear weapons, and not just because he has been around them for so long.

Carter is supporting the Obama administration’s plan to modernize the nuclear arsenal, expected to cost up to $1 trillion over the next 30 years. In my experience, when policymakers want to spend a trillion dollars on something, they tend to gloss over any risks that something might pose, such as, in this case, global annihilation.

But while Carter emphasized the physical security of America’s nuclear weapons, he did not downplay their threat.

“I don’t think that any person who understands nuclear weapons could ever change his or her thinking in this regard: They are the single most fearsome and dangerous technology created by humankind,” he said.

So why have them? Carter’s answer, again, was deterrence. Only nuclear weapons can deter nuclear weapons.

“Until someone has an alternative to deterrence as dealing with someone who might use nuclear weapons against you — and we haven’t found, in all those years since the Manhattan Project, any effective defense against nuclear weapons — until those are found, the only defense we have is the threat of retaliation,” he said.

Later in our conversation, he said of nuclear weapons, “The point of having it is to reduce the risk that anybody uses nuclear weapons against us. In that sense, its whole purpose is to reduce risk.”

But there are moments when the risk associated with nuclear weapons increases, even if only incrementally. We are in one such moment now. Partly that is because of the softening lines of deterrence, undermined by new technology and techniques such as cyber and hybrid war.

But it is also because of something particular to nuclear weapons: The US and Russia, which together possess about 90 percent of the world’s warheads, are both upgrading their nuclear deterrents. But nuclear weapons are simultaneously defensive and offensive. So when you strengthen your ability to deliver those weapons, you are increasing the danger you pose to the other side. And that is destabilizing.

The US, for example, is developing a new air-launched cruise missile that can deliver nuclear strikes more quickly and stealthily. From one perspective, the US is merely keeping pace with Russia’s improving missile defense systems, preserving the status quo equilibrium.

But from another, the cruise missile forces Russia to reduce its response time to any perceived attack and to treat any conventional cruise missile launch as a potentially nuclear strike, thus reducing the world’s margin for error and increasing the risk of “triggering a nuclear war at a time of tension,” as British Foreign Secretary Philip Hammond put it.

I asked Carter, whether these sorts of risks are just the cost of maintaining nuclear deterrence.

“Our focus is really on maintaining the nuclear deterrent that we have. We’re not looking to increase its size. We’re not looking to do anything novel or different with it,” he answered.

But he went on, “The Russians are also very rapidly modernizing their own nuclear arsenal. I don’t associate that with what we’re doing. I associate it with the dynamics of their own feelings that nuclear weapons are one of the only things that guarantee their status in the world.”

“They’re fueling their own nuclear modernization,” he stressed. “It’s a mistake to think that we’re fueling it.”

Maybe so, but the United States is still upgrading its nuclear capabilities at a time of rising tension and blurring lines of deterrence between nuclear powers, and with new hardware that even former Defense Secretary William Perry has called “destabilizing.”

Maybe this is simply necessary for maintaining deterrence. But that deterrence does carry risks. And those risks, in an extremely unlikely but not impossible worst-case scenario, include nuclear conflict. These weapons exist to deter, but that only works if the threat to use them is credible.

As Carter put it, deterrence has the word “terror” in it for a reason.