SINGAPORE — President Trump and Kim Jong-un of North Korea headed into their first face-to-face meeting Tuesday, a momentous step in an improbable courtship that has opened a new chapter for the world’s largest nuclear power and the most reclusive one.
Brash, impulsive leaders who only a few months ago taunted each other across a nuclear abyss, Mr. Trump and Mr. Kim had set aside their threats in a gamble that for now, at least, personal diplomacy can overcome decades of distrust.
In a carefully choreographed encounter, Mr. Trump and Mr. Kim were expected to greet each other in the reception room of a Singapore hotel built on the site of a British colonial outpost — the first time a sitting American president and North Korean leader have ever met.
After photographs, the two men, alone except for their interpreters, were scheduled to meet privately to try to resolve the crisis over North Korea’s nuclear program.
Whether they will succeed is, of course, highly questionable. Their negotiators failed to make much headway in working-level meetings beforehand, leaving Mr. Trump and Mr. Kim with little common ground ahead of what could be months or even years of talks.
But this is a negotiation that follows no known playbook: Two headstrong men — one 34 years old, the other 71; products of wealth and privilege, but with lives so unlike each other that they could be from different planets — coming together to search for a deal that eluded their predecessors.
“I just think it’s going to work out very nicely,” Mr. Trump said on Monday, with the confident tone he has used from the moment in March when he accepted Mr. Kim’s invitation to meet.
Even as he spoke, American and North Korean diplomats were struggling in a last-minute negotiation to bridge gaps on some of the most basic issues dividing the two sides, including the terms and timing under which the North would surrender its nuclear arsenal.
The goal of the negotiators was to lock down the language of a joint communiqué to be issued by Mr. Trump and Mr. Kim at the end of their meeting. If robust and detailed, such a statement could serve as a road map for future negotiations between the sides — and proof that this meeting was more than a mere photo opportunity.
At least 2,500 journalists from around the world were on hand to chronicle what some officials said would amount to an extravagant meet-and-greet exercise. Even if successful, Secretary of State Mike Pompeo predicted, it would only inaugurate a lengthy, complicated and risky process.
Still, the meeting between Mr. Trump and Mr. Kim represents a turnaround that would have been inconceivable just a few months ago, when both men were hurling insults at each other and threatening a nuclear conflict that rattled friend and foe alike.
In the last year alone, Mr. Kim has conducted his nation’s most powerful nuclear test and developed missiles capable of striking American cities. Mr. Trump responded by threatening to unleash “fire and fury like the world has never seen.”
A sudden change in tone started in January, when Mr. Kim, in a gesture of reconciliation, offered to send athletes to the Winter Olympics in South Korea. It was the beginning of a public relations makeover for the young dictator, who only a few months later invited Mr. Trump to meet with him.
Both sides are now considering a formal end to the Korean War, putting to rest a Cold War-era conflict that by some estimates killed five million people.
The communiqué at the conclusion of their meeting is likely to have three sections — on denuclearization, security guarantees for the North and steps to be taken by both sides — according to a person briefed on the talks. But it was not clear that the Americans succeeded in extracting a more detailed commitment to disarmament than North Korea had offered in talks with previous administrations.
On Monday, the White House reverted to tried-and-true diplomatic language, saying it sought complete, verifiable and irreversible denuclearization “on the Korean Peninsula” — a phrase first used in 1992, in a joint declaration between North and South Korea. It had earlier insisted on complete, verifiable and irreversible denuclearization.
North Korea has in the past interpreted the phrase “on the Korean Peninsula” as requiring the United States to scale back American troop deployments in South Korea or even to shrink its so-called nuclear umbrella over two East Asian allies, South Korea and Japan.
Mr. Pompeo insisted on Monday, before Mr. Trump’s meeting, that the administration’s policy had not changed. But he confirmed that the United States would offer security assurances that were different from previous American offers under Presidents George W. Bush and Bill Clinton. He declined to outline them.
“We’re prepared to take actions that will provide them sufficient certainty that they can be comfortable that denuclearization isn’t something that ends badly for them — indeed, just the opposite, that it leads to a better, brighter future for the North Korean people,” he said.
“The concept for these discussions is radically different than ever before,” Mr. Pompeo said.
That is largely because of the personal involvement of Mr. Trump and Mr. Kim, both mercurial figures with a penchant for self-promotion and a hunger to be actors on the world stage. It is also because of the progress North Korea has made in the past year with its arsenal, especially the development of a missile that can strike the mainland United States.
Singapore’s government has turned this futuristic city-state into a giant stage for Mr. Trump and Mr. Kim. In addition to their one-on-one meeting, they were scheduled to meet with their aides at their sides and again over lunch — all at a well-guarded luxury hotel on the island of Sentosa, where tourists and locals visit the Universal Studios theme park or the crescent-shaped beach.
On Tuesday evening, after Mr. Trump speaks to the news media, he plans to depart for Washington, earlier than originally expected.
The White House attributed the schedule change to how quickly it anticipated the diplomacy to wrap up. But it also may be an implicit admission that with so many gaps, the two men may have little to talk about at this meeting.
For Mr. Trump, Monday was a brief intermission between the tumult of an acrimonious Group of 7 meeting in Canada over the weekend and the looming spectacle of his encounter with Mr. Kim.
Mr. Trump stayed largely out of sight in the Shangri-La Hotel, where he has been closeted with aides since landing in Singapore on Sunday evening. Less than a mile away, as if in a rival armed camp, Mr. Kim billeted at his own equally fortified hotel, the St. Regis.
But on Monday evening, Mr. Kim went out on the town. Engaging in some role reversal with Mr. Trump, he visited the Marina Bay Sands Hotel, a striking resort owned by the Las Vegas casino magnate Sheldon G. Adelson. He took selfies with Singaporean officials.
Mr. Trump, meanwhile, refused to let go of his rancorous clash with European allies over trade. On Monday morning, from his hotel, he unleashed a fusillade of angry posts on Twitter about what he said were the predatory trade practices of Canada and several European countries.
“Sorry, we cannot let our friends, or enemies, take advantage of us on Trade anymore,” the president said in a tweet. “We must put the American worker first!”
Mr. Trump’s harsh words about the nation’s closest allies stood in stark contrast to his expression of sunny feelings toward Mr. Kim, a brutal dictator who threatened the United States with a nuclear attack, traded bitterly personal insults with Mr. Trump, and ordered the execution of his own uncle.
“Great to be in Singapore, excitement in the air!” tweeted Mr. Trump, before setting foot outside his hotel.
To negotiate the terms of the joint statement, the administration recruited Sung Y. Kim, a seasoned North Korea negotiator now serving as American ambassador to the Philippines, to lead that effort. Ambassador Kim and a small group of diplomats held a series of talks last week with the North Koreans in the town of Panmunjom, the so-called truce village in the Demilitarized Zone between North and South Korea.
People briefed on the meetings said American negotiators had found it difficult to make significant headway with the North Koreans, in part because the White House did not back them up in taking a hard line.
In his public statements, Mr. Trump has shown gradually greater flexibility toward North Korea, saying he viewed its disarmament as a “process,” rather than something to be done all at once, and disavowing the phrase “maximum pressure,” after making it the centerpiece of his policy.
Mr. Pompeo took issue with a report in The New York Times that Mr. Trump would be handicapped in the negotiations because of a lack of scientists on his negotiating team. He said the government could draw on the expertise of dozens of Ph.D.’s in nuclear, chemical and biological weapons.
“Any suggestion that the United States somehow lacks the technical expertise across government, or lacks it on the ground here in Singapore, is mistaken,” Mr. Pompeo said.
Some foreign-policy experts said the breakdown at the Group of 7 meeting might play to North Korea’s advantage, since Mr. Trump can ill afford a second failed summit, back to back. The president has consistently predicted success, even as his definition of that has grown foggier.
But other analysts said Mr. Kim was as determined as Mr. Trump to make this meeting a success. That, as much as Mr. Trump’s need for a victory after Canada, may guarantee a positive outcome.
“Kim and Trump both seem to want the same thing,” said John Delury, a professor of Chinese studies at Yonsei University in Seoul. “A dramatic reversal in the U.S.-North Korea relationship, which can be attributed to their vision.”
South Korea’s president, Moon Jae-in, who worked intensely to help broker the meeting, underlined its historic nature.
Mr. Moon urged a “bold give-and-take” to make it successful. But he said that regardless of whatever agreement was produced, it would be just the beginning of what could be a long, bumpy process of ridding North Korea of a nuclear arsenal it has spent decades building.
“Even after the two heads of state open the gate,” Mr. Moon said, “it will take a long process to achieve a complete solution. We don’t know how long it will take: one year, two years or more.”