“I said a long time ago that maybe I’ll be a sleeper on foreign policy,” Mr. Trump noted in a Saturday afternoon news conference in Osaka. He later added, “I am really the opposite of a warmonger.”

For his part, Mr. Kim has strong incentives to remain friendly with Mr. Trump. While many experts, and more than one senior Trump administration official, are convinced that he will never willingly give up his nuclear weapons, Mr. Kim can enhance his stature at home and find more legitimacy on the world stage by meeting with Mr. Trump.

Mr. Kim may also be motivated by the American political calendar, which United States officials and analysts say his government analyzes carefully.

“From Kim’s perspective, Trump is still the best possible president to make a deal with, since it is highly unlikely that the next U.S. president would put on the negotiating table big-ticket items that the North has always sought, such as a peace treaty,” said Sue Mi Terry, who served as a National Security Council aide specializing in Korean affairs under both Presidents George W. Bush and Barack Obama.

But another encounter would bring risks for both men. Mr. Kim was embarrassed by the breakdown of talks in Hanoi after he had taken a train journey of 70 hours to meet with Mr. Trump. He has also said the United States must present “a new calculation” before he would return to formal talks.

But there is no sign that Mr. Trump has softened his negotiating position since he rejected Mr. Kim’s offer in Hanoi to dismantle just one of his country’s many nuclear facilities in return for sanctions relief.

And Mr. Trump himself acknowledged that he had stuck out his neck with his solicitous tweet. In his Saturday news conference, he acknowledged that he knew when he posted his invitation on Twitter that if Mr. Kim didn’t trek the approximately 100 miles from the North Korean capital of Pyongyang to the border, “everyone was going to say, ‘Oh, he got stood up.’”