Donald Trump plays the media like a fiddle. This Ted Cruz birther flap proves it.

Amazingly enough, “birther” questions about Ted Cruz’s qualifications for the presidency have suddenly become mainstream in the GOP.

On Wednesday, two leading Republicans — including John McCain, the party’s 2008 presidential nominee — questioned whether Cruz’s Canadian birthplace makes him ineligible for the nation’s highest office.

“There is a question,” McCain said in an interview with the Steve Merrill Show (via Andrew Kacyznski of BuzzFeed News), about whether Cruz’s birth “on foreign soil” disqualifies him. “I am not a constitutional scholar on that,” McCain continued. “But I think it’s worth looking into! I don’t think it’s illegitimate to look into it!”

That same day, Rand Paul — who, of course, is running against Cruz — made similar remarks on another radio show. He said he was “not an expert,” that “people have various opinions,” and that the Supreme Court hasn’t settled the issue. (He also joked that Cruz was “without question” qualified — to be prime minister of Canada.)

As Vox’s Dara Lind explained, the consensus among legal scholars is clear that Cruz is, in fact, perfectly eligible to run (he gained birthright citizenship through his mother, who was a US citizen).

But McCain and Paul are picking up a ball tossed by — who else? — Donald Trump. With just one comment on Tuesday night, Trump has managed to place a fringe, conspiracy theory–esque topic at the center of the political conversation — getting the media and even leading Republicans to dance to his tune, and spreading some old-fashioned xenophobia about the man who’s currently his most dangerous rival.

Ted Cruz is beating Donald Trump in Iowa. He’s been on the rise in national polls. He’s been winning some key Christian right endorsements. And his operation has raised a ton of cash.

So the famously selfless Trump has naturally started to worry that if Cruz is nominated, he could face legal challenges about his qualifications that could damage the Republican Party. (Trump cares deeply about the party.) Here’s what Trump told the Washington Post’s Robert Costa and Philip Rucker in a Tuesday evening interview:

TRUMP: “Republicans are going to have to ask themselves the question: ‘Do we want a candidate who could be tied up in court for two years?’ That’d be a big problem It’d be a very precarious one for Republicans because he’d be running and the courts may take a long time to make a decision. You don’t want to be running and have that kind of thing over your head.”

Now, Trump was careful to avoid saying that he didn’t think Ted Cruz was eligible. Indeed, he distanced himself from that position on Thursday with some helpful “advice” to Cruz that is not at all genuine and really just another excuse for him to bring up the issue:

Trump knows the power of his words. And he knows the power of injecting a fringe idea into the media bloodstream. Recall that back in 2011, Trump was the highest-profile figure in the “birther” movement, which questioned whether President Obama was truly born in the US. This is what built his popularity among the far right and convinced him he could make a serious run for the presidency.

So it’s no surprise that members of the media would jump on Trump’s insinuation and begin asking every Republican under the sun what he or she thought about it. That’s expected at this point — and, indeed, quite defensible, considering Trump is the top-polling Republican and his positions matter.

Yet time and again, Trump has exploited this dynamic to promote himself and spread sleaze about his opponents. By saying things that go beyond the bounds of normal political discourse, he guarantees that the media (including us!) will cover his hot, outrage-inducing story and dance to his tune.

It may be a bit more surprising, though, that someone like McCain would play along this time. Indeed, McCain faced questions about his own eligibility when he ran in 2008, since he was born in the Panama Canal Zone. But in his radio appearance, he took pains to point out that Cruz’s situation was different, since he was born on “foreign soil.”

MCCAIN: I do not know the answer to that [whether Cruz is qualified]. I know it came up in my race because I was born in Panama but I was born in the Canal Zone when it was a territory... It’s a US military base. That’s different from being born on foreign soil. So I think there is a question. I am not a constitutional scholar on that. But I think it’s worth looking into! I don’t think it’s illegitimate to look into it!

The background here is that, like most other Republican senators, McCain utterly loathes Cruz and views him as an arrogant blowhard. Just months after Cruz joined the Senate, McCain was already calling him one of the “wacko birds.“ And earlier this year, McCain gleefully mocked Cruz’s claim that he was “pressing” McCain to hold hearings on a gun policy change. “It came as a complete surprise to me that he had been pressing me. Maybe it was some medium that I’m not familiar with. Maybe bouncing it off the ozone layer, for all I know.”

The irony, of course, is that Cruz would likely be a far more acceptable nominee for GOP elites than Trump — he’s much closer to them on most major issues, and far less of a loose cannon. So by shivving Cruz, McCain is doing Trump’s work for him.