Among the skeptics is Mr. Trump’s new secretary of state, Mike Pompeo, who made a secret visit to Pyongyang over Easter weekend to try to gauge Mr. Kim’s sincerity. Last summer, it was Mr. Pompeo, then still the C.I.A. director, who argued that the only way to deal with North Korea was to separate Mr. Kim from his weapons, a comment some interpreted as advocating regime change.

On Friday at NATO, on his first full day as secretary of state, Mr. Pompeo suggested for the first time that the North Korean leader was ready to deal. “I did get a sense that he was serious,” he told reporters. “The economic pressure that has been put in place by this global effort that President Trump has led has led him to believe that it’s in his best interest to come to the table and talk about denuclearization.”

Yet talking is different from denuclearizing. And talking about denuclearizing is hardly new. The North promised the same in a 1992 agreement, and many in Seoul, the South’s capital, wondered then if the nightmare of living under the constant threat of artillery barrage was about to end. In fact, the agreement reached on Friday picks up language from the 1992 accord, and has similar provisions about reuniting families separated during the Korean War and nonaggression agreements. Little of it happened.

There were two agreements with the George W. Bush administration, each described at the time as breakthroughs. Since then the North has amassed 20 to 60 nuclear weapons, up from zero when those commitments were made.