In the process, Mr. Trump is upending the usual sequence of events in diplomacy: beginning with a leader-to-leader summit meeting, and then leaving the details to underlings.

What is most remarkable, however, is that Mr. Trump agreed to the meeting on an impulse in March, pulled out of it a week ago after reacting to threats in a North Korean statement, and now has restored it without obtaining, at least in public, even the minimum concessions of the kind that North Korea made a decade ago.

Without question, Mr. Trump has gotten farther with North Korea than any American president since that time. Until recently, White House officials said that was because of his laser focus on harsh sanctions and his threat to use military force, giving the United States leverage it never had before.

But in the past few days, trying to coax the North Koreans to keep the June 12 meeting on the calendar, Mr. Trump now risks making Mr. Clinton’s mistake: an agreement so thin and slow to execute that Mr. Kim may be able to run the play his father and grandfather mastered — giving just enough ground to weaken the sanctions on the North, waiting things out, then looking for a way to resume the fastest-developing nuclear program on earth.

Indeed, Mr. Trump appears more willing to make concessions to North Korea than he is to Iran, which has a small fraction of the North’s nuclear infrastructure, and no nuclear weapons. That may partly reflect the fact that ending the threat from North Korea is Mr. Trump’s bid for history, much as Iran was Barack Obama’s bid.

Mr. Trump’s concessions, some people involved in those past negotiations said, are also a sign that he recognizes the realities of dealing with a suspicious, reclusive government that is wedded to its nuclear shield.

The president’s evolution toward a more conventional approach was dictated by events he helped set in motion, Mr. Cha said. The diplomatic thaw initiated by Mr. Kim and South Korea’s president, Moon Jae-in, and endorsed by Mr. Trump, has already weakened the sanctions regime he spent more than a year marshaling.