Trump’s pique with South Korea might be explained by an embarrassment he had suffered in the country two weeks earlier. Apparently misunderstanding a Pentagon briefing, Trump had boasted in an April 12 Fox Business interview that he was personally and immediately sending a “very powerful” “armada” into Korean waters to menace North Korea. That armada—the aircraft carrier USS Carl Vinson and support vessels—was then photographed thousands of miles away heading in the opposite direction, passing between the Indonesian islands of Java and Sumatra en route toward India. Trump’s mistake was criticized by South Korean politicians and mocked in the South Korean media. The Reuters interview may have been payback.

That interview had the unintended effect of helping to boost the more U.S.-skeptical of the South Korean presidential candidates in the May 9 election. In midsummer, speaking at his New Jersey golf retreat without a single South Korean present, Trump promised to visit “fire and fury like the world has never seen” upon North Korea. In September at the United Nations he warned that he might “totally destroy North Korea,” adding “Rocket Man is on a suicide mission for himself and his region.”

As a candidate for president, South Korea’s Moon Jae In had opposed the deployment of missile defenses, urging negotiation with the North instead. Now as president, this conciliation-minded leader—already inclined toward skepticism of the United States—daily confronts a new strategic reality: His country’s most important security partner seems determined to confirm every negative attitude about the U.S. held by nationalist South Koreans. The Moon government has responded with a flurry of overtures toward the North.

Together, Kim Jong Un and Donald Trump are enabling the North Korean nuclear program to evolve into a mighty diplomatic weapon against U.S. interests, separating South Korea from the United States, incentivizing the South to placate the North. Together, Kim and Trump are depriving the U.S. of conventional military options—because there is no non-nuclear option against the North without the support of the South. Between 2015 and 2017, South Korean confidence in the United States to do the right thing in international affairs has dropped by a startling 71 points in a Pew survey. Only 17 percent of South Koreans have confidence in Donald Trump—less than half the number that trust China’s Xi Jinping.

And who is Xi’s best publicist? Why, Donald Trump himself. Trump has often told the world that it is China, not the United States, that has the most leverage over North Korea. He tweeted in 2013, “North Korea is reliant on China. China could solve this problem easily if they wanted to but they have no respect for our leaders.” And as president too, he has looked to China first and foremost to sway North Korea. He tweeted in July 2017: “Perhaps China will put a heavy move on North Korea and end this nonsense once and for all!”