“There’s not any starry-eyed feeling among the group doing this,” John R. Bolton, the national security adviser, insisted Sunday on CBS’s “Face the Nation,” saying that most of the major steps toward denuclearization could be taken in a year. In private, Trump administration officials say, Mr. Bolton’s view is the same as it was before he joined the administration: that the North Koreans will never entirely give up their program.

The big question is whether Mr. Kim is truly ready to change course or playing for time with Mr. Trump — as his father and grandfather did with the past four presidents.

Meanwhile, Mr. Trump is in sales mode.

Frustrated by the series of reports that the North is chugging forward, despite its “denuclearization” pledge, Mr. Trump boasted in a tweet on Tuesday that there had been “no Rocket Launches or Nuclear Testing in 8 months. All of Asia is thrilled. Only the Opposition Party, which includes the Fake News, is complaining.”

Then, with a Trumpian flair, he added, “If not for me, we would now be at War with North Korea!”

Mr. Trump is at least partly right: There have been no missile or nuclear tests since November, a freeze that many, including some Democrats, said was a necessary first step. But a freeze and denuclearization are completely different things.

Mr. Kim retains all of his nuclear abilities, and thus his leverage. He can resume testing any time. Just a year ago, Rex W. Tillerson, then the secretary of state, called that position insufficient because it merely perpetuated an ability to strike that Mr. Trump had, until recently, characterized as intolerable.

But it also reveals, in perhaps the most critical national security crisis Mr. Trump faces, his tendency to conflate a good meeting with a good outcome. It is as if President John F. Kennedy, meeting with the Soviet Union’s Nikita Khrushchev for the first time in Vienna in 1961, had declared the Cold War solved. The Cuban missile crisis broke open 16 months later.

Mr. Kim has already accomplished something, too. The heat has been turned down drastically, and the United States has, unilaterally, suspended military exercises with South Korea.