For Mr. Trump, diplomacy with North Korea has always been about theater and politics. In falsely declaring after his first summit with Mr. Kim that “there is no longer a nuclear threat from North Korea,” while bragging that the risk of war — which he foolishly stoked — is now diminished, the president is intent on creating the illusion of progress. In fact, there has been none toward our core goal of full denuclearization.

Mr. Trump instead touts his love of Mr. Kim at campaign rallies and generates Nobel Peace Prize nominations for himself with the aim of convincing his political base that he is a diplomatic genius. If he can punt the complex North Korean nuclear threat to the end of his presidency without being disturbed by new tests, Mr. Trump would seem content to claim victory and leave the problem to his successors.

Thus, the risk of the Hanoi summit is twofold. First, in a rush to generate good optics and distract from unpleasant developments at home, Mr. Trump may make further concessions to the North Korean dictator, like a peace declaration, partial sanctions relief, or continued limitations on United States military exercises or troop presence without receiving tangible, irreversible concessions in return. Second, Mr. Trump risks squandering an opportunity to make real headway toward denuclearization.