Mr. Kim arrived early for the summit meeting as a sign of respect for his counterpart, who is more than twice his age. Mr. Trump played the role of the elder host, gently guiding Mr. Kim to the meeting room, showing him his limousine and reporting to the news media about the good-natured flavor of the meetings. Those personal touches in summit diplomacy can create unique opportunities for trust-building that a normal diplomatic démarche cannot.

To be sure, the joint statement that Mr. Trump and Mr. Kim released after their meeting left a lot to be desired. Mr. Kim did not commit to verifiable and irreversible dismantlement of North Korea’s nuclear programs. Mr. Trump gave props to a dictator who, according to the United Nations, belongs in a docket before the International Criminal Court for crimes against humanity. Mr. Trump surprised his South Korean ally by announcing that he would cancel joint United States-South Korea military exercises that help to keep the peace on the Korean Peninsula. The photo opportunity of a face-to-face meeting with the leader of the free world is the ultimate legitimizer for this nuclear rogue state.

Yet, in the case of North Korea, there are never good policy options — there are only choices between the bad and the worse.

Mr. Trump’s diplomacy, however unconventional, has pierced the isolation bubble of the North Korean leadership, which no previous president could do. The Singapore meetings will be remembered in North Korea’s domestic narrative as Mr. Kim’s coming-out party as the leader of the world’s newest nuclear-weapons-armed state. But the United States has set the agenda for next steps, with follow-up talks led by Secretary of State Mike Pompeo. And Mr. Trump has implicitly set the autumn as the first deadline for some deliverables with the promise of an invitation to the White House, presumably on the sidelines of the United Nations General Assembly in September.

Mr. Trump now needs to get North Korea to provide a full declaration of its nuclear weapons that will be verified by international inspectors. After verification, Mr. Kim must begin a process of dismantling and removing his weapons at a point in the future. The international community, despite its ambivalence to Mr. Trump, will have to support the American president in holding the North to these obligations.