By Anna Fifield, Joby Warrick, Washington Post–

A team of U.S. officials crossed into North Korea on Sunday for talks to prepare for a summit between President Trump and Kim Jong Un, as both sides pressed ahead with arrangements despite the question marks hanging over the meeting.

Sung Kim, a former U.S. ambassador to South Korea and former nuclear negotiator with the North, has been called in from his post as envoy to the Philippines to lead the preparations, according to a person ­familiar with the arrangements.

The talks are focused on what would be the substance of a potential summit between Trump and Kim Jong Un — the issue of North Korea’s nuclear weapons program.

After Saturday’s surprise ­inter-Korean talks, South Korean President Moon Jae-in said Kim was still committed to the “complete denuclearization” of the Korean Peninsula. But Moon declined to define “complete de­nuclearization,” suggesting that there are still fundamental gaps on the key issue bedeviling preparations.

Crossing the line that separates the two Koreas, Sung Kim met with Choe Son Hui, the North Korean vice foreign minister, who said last week that Pyongyang was “reconsidering” the talks. The two officials know each other well — both were part of their respective delegations that negotiated the 2005 denuclearization agreement through the six-party framework.

The meetings were trumpeted by Trump later Sunday afternoon, when he tweeted, “Our United States team has arrived in North Korea to make arrangements for the Summit between Kim Jong Un and myself. I truly believe North Korea has brilliant potential and will be a great economic and financial Nation one day. Kim Jong Un agrees with me on this. It will happen!”

The talks are expected to continue Monday and Tuesday at Tongilgak, or “Unification House,” the building in the northern part of the demilitarized zone where Kim Jong Un met Moon on Saturday. That impromptu session was aimed at salvaging the summit that Trump had said he was scuppering just two days earlier.

The South Korean president, who is playing something of a mediator role in the talks, was optimistic afterward. “We two leaders agreed the June 12 North Korea-U.S. summit must be successfully held,” he said.

‘They’re playing a game’

In Washington, lawmakers and former U.S. intelligence officials expressed general support Sunday for proceeding with the summit, but many reacted skeptically to North Korea’s suggestion that it is open to discussing denuclearization.

“They’re playing a game,” Sen. Marco Rubio (R-Fla.), a member of the Senate Foreign Relations Committee, said on CBS’s “Face the Nation.” “Kim Jong Un — these nuclear weapons are something he’s psychologically attached to. They are what give him his prestige and importance. . . . I’d love to see them denuclearize. I just, I’m not very optimistic about that.”

James R. Clapper Jr., the former director of national intelligence and a onetime senior intelligence officer for U.S. forces in South Korea, said he worried that North Korea’s idea of “denuclearization” entails scaling back or eliminating U.S. strategic forces in the Pacific.

“When we say ‘denuclearization of the Korean Peninsula,’ this could be a two-way street,” Clapper said, also on “Face the Nation.”

Clapper suggested that a worthy goal for the summit might be to establish a “regular conduit for communication” between the two countries, perhaps including the opening of diplomatic interest sections in both capitals.

“This is not a reward for bad behavior at all,” Clapper said. “It’s mutually reciprocal and would give us that presence there, more insight and more understanding.” From North Korea’s point of view, he said, a U.S. presence in the country might give Pyongyang a “sense of security” against a possible U.S. attack.

a man wearing glasses and smiling at the camera© Provided by WP Company LLC d/b/a The Washington PostBut Michael V. Hayden, CIA director during the George W. Bush administration, said he worried that Trump might be at a disadvantage in a face-to-face negotiation with Kim Jong Un.

“I don’t know the president has done the kind of homework that would allow him to do this,” Hayden said on “Fox News Sunday.” Hayden said the “real danger” is not the rhetoric and theatrics surrounding the meeting, but rather the substance: “What will happen at this meeting?”

“These folks are not going to get rid of all their nuclear weapons,” Hayden said. “And if President Trump’s brand — and that’s the right word here, going into this meeting — demands something like that, this is going to end up in a very bad place.”

Diplomat’s help hailed

Given all the ups and downs with the summit, many analysts were relieved to hear that the administration had enlisted Sung Kim to help, especially given the retirement of fellow seasoned diplomat Joseph Yun earlier this year.

“This is a great step,” said Vipin Narang, a nuclear nonproliferation expert at the Massachusetts Institute of Technology, noting that the summit preparation was best handled by experts behind the scenes rather than in public forums such as Twitter.

“This is how progress is made, and the best chance to have a summit, and one that yields meaningful outcomes,” Narang said.

Sung Kim was joined by Allison Hooker, the Korea specialist on the National Security Council, and Randall Schriver, the assistant secretary of defense for East Asia and one of the officials who accompanied Secretary of State Mike Pompeo to Pyongyang earlier this month.

Sung Kim, who was born in South Korea and was a key diplomat in the 2005 six-party talks, served as ambassador to South Korea from 2011 to 2014, then became special representative for North Korea policy, a position that Yun later took over and that is now vacant.

His North Korean counterpart, Choe, also has years of experience working on these issues and is well connected within the North Korean hierarchy.

She has also served as a nuclear negotiator and led the division for U.S. affairs in the North Korean Foreign Ministry until being promoted to vice foreign minister this year. The daughter of a former premier, she is thought to have direct access to Kim.

Denuclearization doubts

Most analysts say it is extremely unlikely that North Korea will surrender its nuclear weapons. The United States has been pushing for “complete, verifiable and irreversible dismantlement” — a high bar that would require North Korea to relinquish its entire nuclear program and allow verification by international inspectors.

North Korea, which refers to its nuclear weapons program as its “treasured sword” keeping the country safe, has repeatedly said it is not interested in unilateral disarmament.

Still, a summit might be able to narrow the gap. “This is an opportunity to find out what, in fact, they might be willing to do and vice versa — and that is the most important step right now,” Narang said.

The April 27 inter-Korean summit, which produced a vague declaration to work toward denuclearization and a peace treaty for the Korean Peninsula, was meant to serve as a springboard for talks between U.S. and North Korean leaders.

Trump surprised the South Koreans in March by hastily agreeing to meet Kim in a summit, which would be the first such meeting between a sitting American president and a North Korean leader.

But the preparations have become increasingly tumultuous as the summit date draws nearer.

After North Korean officials, including Choe, lashed out at Vice President Pence and national security adviser John Bolton, Trump abruptly announced that he was canceling the talks, citing North Korea’s “tremendous anger.”

But after a magnanimous statement from North Korea that said Kim still hoped to meet Trump “at any time,” the summit appears to be on again.

“We are having very productive talks with North Korea about reinstating the Summit which, if it does happen, will likely remain in Singapore on the same date, June 12th., and, if necessary, will be extended beyond that date,” Trump tweeted Friday night.

The White House has said that preparations will continue while the final decision on whether to proceed with the summit is made.

Trump confirmed Saturday that working-level meetings were continuing. “As you know, there are meetings going on as we speak in a certain location, which I won’t name, but you’d like the location,” he told reporters in Washington.

A separate U.S. team led by Joe Hagin, deputy chief of staff in the White House, is organizing logistics with Kim Chang Son, who is effectively the North Korean leader’s chief of staff.

Kim Chang Son was in Beijing from Thursday to Saturday, according to Japanese and South Korean media reports, although it was not clear whether his trip was related to the summit preparations.

Warrick reported from Washington.