Trump blamed China for North Korea. Then he changed his mind. Then he changed it again.

On Friday, North Korea tested a missile that could theoretically hit New York and Washington, DC, the first time it’s ever tested a missile with that kind of range. On Saturday night, President Trump tweeted something of a response to this very serious threat — blame China:

There is a certain kind of logic here: China is North Korea’s largest trading partner by far, so Beijing really does have economic leverage over Pyongyang. If China were to put more pressure on North Korea, this could — as the president says — help get North Korea to the negotiating table.

But experts say that, contra Trump, China can’t “solve” the North Korea nuclear crisis on its own. North Korea is not just going to give up its nuclear program because Beijing says so.

“Sure, China has some economic leverage, but its political influence has limits,” Jenny Town, the assistant director of the US-Korea Institute at Johns Hopkins University, tells me via email. “Believing China has some secret power over North Korea is just wishful thinking.”

Trump’s new tweets also flagrantly contradict his line from just one month ago — when he thanked China for its efforts with North Korea:

What this all shows, most fundamentally, is that Trump’s North Korea policy makes no sense. It keeps changing in a way that reflects the president’s own mercurial nature and lack of detailed policy knowledge. It is the precise opposite of the kind of careful diplomacy you’d need to enlist China’s help against North Korea.

“Trump’s concept that ‘China could easily solve this problem’ shows a fundamental lack of understanding of this challenge,” explains Laura Rosenberger, the former National Security Council director for Korea and China. “Vague demands and nonspecific threats are not going to move the Chinese.”

Trump had taken aggressive stances on China for years prior to taking office, particularly on the issue of trade. During the campaign he claimed China was “ripping us left and right” and suggested, somewhat strangely, that he’d “take ’em to McDonald’s and go back to the negotiating table!”

This skepticism about China colored the early months of Trump’s presidency, particularly when it came to North Korea. In March, for example, he slammed China on Twitter for failing to assist (much like he did this weekend):

In an interview with the Financial Times published on April 3, Trump demanded that China fix North Korea or else face the threat of some (unspecified, but by implication military) US action.

“If China is not going to solve North Korea, we will. That is all I am telling you,” he said. “China will either decide to help us with North Korea, or they won’t. And if they do that will be very good for China, and if they don’t it won’t be good for anyone.”

Then Trump welcomed Chinese President Xi Jinping to his estate at Mar-a-Lago on April 6 — and everything changed. By the president’s own account, as told to the Wall Street Journal, the two men briefly chatted about the history of Chinese-Korean relations. The conversation rocked Trump’s world.

“After listening for 10 minutes, I realized it’s not so easy,” the president told the Journal. “I felt pretty strongly that they had a tremendous power [over] North Korea. ... But it’s not what you would think.”

Town called Trump’s approach to North Korea “naive” in our correspondence, and this is a perfect example of what she’s talking about. The president claims to have come to a profound realization about one of the most dangerous conflicts on earth after a 10-minute conversation with the leader of North Korea’s chief patron, which also happens to be the United States’ chief rival in East Asia.

In any event, the conversation with Xi seemed to have really shaped the way that the president thought about China’s approach to the North — hence the tweet in June thanking Xi for his efforts. Now he seems to have come back around to his original position yet again, for reasons that are not fully clear.

In Trump’s defense, his new/original stance is more accurate than the post-Xi meeting one. China has done a bit to pressure Pyongyang, like ramping up criticism of the North in state-run media outlets, but that hasn’t caused Kim Jong Un to change course on any major issue (at least, as far as we can tell). Moreover, trade between China and North Korea actually increased in the first quarter of 2017, suggesting Beijing isn’t seriously trying to use economic pressure — by far its biggest stick when it comes to the North.

But by taking so many different positions, and shifting between them so rapidly, the president has undermined whatever ability the United States might have had to actually get the Chinese to ramp up pressure.

“[Moving Beijing] requires a comprehensive and carefully executed strategy that includes specific asks and clear consequences for inaction,” Rosenberger tells me. “Members of Trump’s administration have tried to put in place the kind of comprehensive strategy we need, building on the Obama administration’s efforts toward the end of his second term, but President Trump and his shoot-from-the-hip [T]witter statements are undermining that very effort.”

It’s important not to dance around the root cause of the problem here: the president’s lack of actual policy opinions. This is a man who, three months into his presidency, admitted publicly that the Chinese president convinced him to change his mind on one of the world’s most important crises. Trump does not know very much about North Korea and seems to base his opinion on whatever he feels.

It’s impossible for the United States to have a cogent approach toward the Korean Peninsula when the president keeps tweeting out contradictory policy stances.

“It’s clear that President Trump does not understand North Korea or the complexity of the situation,” Town writes. “Until Trump takes this issue seriously and takes the time to actually learn/recognize what North Korea’s strategic concerns and interests are and start to build a policy that addresses them, not just look for quick fixes, the situation will continue to deteriorate.”