The essence of sumo is simple: two enormous men struggle to throw each other out of a ring. On Sunday, U.S. President Donald Trump attended a sumo tournament in Tokyo with Prime Minister Shinzo Abe, awarding the new President's Cup to the winner. The metaphor was obvious: Throughout his state visit, Trump was like a sumo wrestler who Abe desperately wanted to move on key policy positions, but the president wasn't budging. The most important of these disagreements is over Asia's biggest immediate threat, North Korean dictator Kim Jung Un.

In assessing North Korea's recent launch of several short-range ballistic missiles, Trump simply waved them off, saying it "disturbed some of my people," but he wasn't worried. Those "people" include his own intelligence community and national security adviser John Bolton, who had called the launches significant violations of U.N. sanctions. Trump's blase attitude also ran contrary to the views of his Japanese hosts, who are directly threatened by Kim's shorter-range missiles. This mistake on the president's part will have unfortunate knock-on effects.

Most worrisome is the potential effect on the Japan-U.S. alliance. Tokyo wants help on a range of geopolitical, economic and trade fronts. These include support in its territorial dispute with China over the Senkaku Islands in the East China Sea, which is threatening to heat up; buying more advanced military hardware; continued ability to sell in U.S. markets, especially automobiles; more pressure on Kim to return Japanese citizens abducted by his regime; and — above all — solidarity on stopping Kim's nuclear weapons and ballistic missile programs.