That envoy, Special Representative Stephen Biegun, is now saying Kim committed to destroying plutonium and uranium enrichment facilities, even though he conceded the two sides have not publicly agreed on what "denuclearization" means -- the commitment made at the leaders' first summit last summer.
Earlier this week, U.S. intelligence agencies said they assess North Korea is unlikely to give up all of its WMD stockpiles, delivery systems, and production capabilities because its leaders view nuclear arms as critical to the regime's survival.
But Trump said the summit is on regardless, touting "tremendous progress" in the administration's talks with North Korea and telling reporters in the Oval Office that the where and when of the meeting would be announced next week.
"Most of you know where that location is. I don't think it's any secret," he said about the summit, adding the timing will be "the end of February." He later suggested he would reveal those details in his State of the Union address on Tuesday.
Secretary of State Mike Pompeo confirmed on Wednesday that the meeting will be "someplace in Asia," while a U.S. official had previously told ABC News that they are zeroing in one of three cities in Vietnam -- Hanoi, Ho Chi Minh City, or Da Nang.
Before they can sit together, however, negotiating teams from both countries will meet again. Biegun will travel to South Korea on Sunday to meet his South Korean and North Korean counterparts, the State Department confirmed Thursday, and in particular, Biegun and North Korea's Amb. Kim Hyok Chol will negotiate the details of Trump and Kim's second joint declaration.
They'll be tasked with "achieving a set of concrete deliverables, a road map of negotiations and declarations going forward, and a shared understanding of the desired outcome of our joint efforts," Biegun said Thursday during a speech at Stanford University.
The document the two leaders signed at the previous one has been criticized for being too vague, and analysts say that the future of diplomatic talks is riding on this meeting to achieve more concrete outcomes.
If not, and diplomatic talks fail, the U.S. does have "contingencies" in place, Biegun said.
But Trump wants this the conflict with North Korea to end, he added, saying, "It is over. It is done. We are not going to invade North Korea. We are not seeking to topple the North Korean regime."
Still, achieving a lasting peace will require North Korea giving up its nuclear weapons, and as U.S. intelligence chiefs said earlier this week, the special envoy conceded, "North Korea has given us little indication that they have yet made the decision to completely dismantle and destroy that capability."
At this point, the two sides still don't even agree on what the term "denuclearization" means, with Biegun saying they need a "detailed," "specific," and "agreed" definition.
In December, North Korea state media released a statement, saying the country would not dismantle its nuclear weapons until the U.S. withdrew its forces from the region -- its clearest definition yet of denuclearization, but something the U.S. has said it will not do.
"We are not involved in any diplomatic discussion, full stop, that would suggest this trade-off," Biegun said of a possible U.S. troop withdrawal from South Korea. "It has never been discussed."
From the U.S. perspective, Biegun said that a "final" denuclearization deal would include "the removal or destruction of stockpiles of fissile material, weapons, missiles, launchers and other weapons of mass destruction" -- the kind of unilateral disarmament Kim has refused. North Korea would also have to provide a "comprehensive declaration" of its weapons of mass destruction and missile programs -- something it has so far refused to do in talks, even sparking outrage among its negotiators during a meeting with Pompeo last July.
The U.S. would also require an agreement on "expert access and monitoring mechanisms of key sites" of its weapons programs, which Pompeo said North Korea agreed to in October but has not yet happened. Biegun said he would push for progress on that again in his upcoming meetings.
While North Korea's public pronouncements do not match all of these U.S. demands, Biegun said that Kim Jong Un made commitments in private. In particular, he said, Kim committed to the "dismantlement and destruction of North Korea's plutonium and uranium enrichment facilities... the totality of North Korean plutonium reprocessing and uranium enrichment programs" when Pompeo met him in Pyongyang in October.
Again, North Korea has not confirmed that, but Kim did agree in September in a joint declaration with South Korean President Moon Jae In to allow inspectors to the nuclear production facility at Yongbyon if the U.S. took "corresponding measures."
Biegun said the U.S. still does not know what those measures would be, but hopes to find out soon.