Washington (CNN) President Donald Trump's claim that he's ready to walk away in the middle of a summit with North Korea underscores the high risks of the unprecedented meeting with Kim Jong Un that is set to take place within weeks.

Trump told reporters at his Mar-a-Lago estate on Wednesday that, "if the meeting when I'm there isn't fruitful, I will respectfully leave the meeting."

The idea of an abrupt, mid-meeting departure comes from Trump's new national security adviser, John Bolton , according to a person familiar with the conversations. Walking out in the middle of the meeting would provide a Trumpian level of theatricality to an already dramatic event, the source said.

But it could also deeply offend a nuclear-capable leader who has issued threats against the US, and short-circuit chances of diplomacy, analysts said.

And Trump is making the assumption that genuine progress could be made -- highly unlikely beyond a prearranged gesture such as a release of Americans being held captive in North Korea -- especially given that the administration is pulling together in weeks the kind of meeting that usually takes years of preparation.

A lot of opportunity and great risk

"The summit itself brings a lot of opportunity at the same time it brings great risk," said Lisa Collins, a Korea Chair fellow at the Center for Strategic and International Studies. "Trump saying, 'I'll just get up and leave,' just demonstrates the risks that are being racked up. He could come out with a peace treaty deal or come out and say, 'We didn't get anything out of this, we're going to return to a more hardline approach.' "

Trump, who has told advisers he's confident in his ability to sway Kim in person, shocked observers with the announcement last month that he'd meet with the North Korean leader despite the concerns of allies such as Japan.

The administration delivered another surprise this week with the news that CIA Director and Secretary of State nominee Mike Pompeo had met with Kim in Pyongyang to prepare for the summit.

The former supreme allied commander of NATO, James Stavridis, said news of Pompeo's trip left him "honestly incredulous," in part because it took so long for the news to come out.

Speaking on the conservative radio show hosted by Hugh Hewitt, Stavridis said he thought there is "about a 70% chance of pulling this thing off diplomatically. But the bad news is I think there's a 30% chance it goes back to the bad old days, and we're back into the danger zone with Kim Jong Un."

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North Korea made a significant gesture, dropping its longtime demand that the US withdraw its forces from South Korea in exchange for denuclearization, South Korean President Moon Jae-in told reporters Thursday.

"North Korea has expressed willingness to give up its nuclear program," according to Moon, without demanding that US troops leave the Korean Peninsula -- "a condition that the US cannot accept."

It's just the latest unexpected and new twist.

"We're in uncharted waters," said Bruce Klingner, a former deputy division chief for Korea at the CIA who's now a senior fellow at the Heritage Foundation. Pompeo's trip was "a surprise in a year of surprises, especially when you think of where we were two months ago, talking about pre-emptive strikes," Klingner said.

The fact that Pompeo has been involved from the beginning, and will likely soon be acting as the top US diplomat "makes it more likely that the US-North Korea summit will occur," Klingner said. "Perhaps there's greater prospects for progress than any of us had realized."

But Pompeo's trip, conducted over Easter weekend, has garnered both praise and condemnation from lawmakers as he faces a confirmation fight.

With concerns that his nomination may be in trouble , the administration and its allies have said Pompeo's visit is evidence of his qualifications and -- to counter the frequent criticism that the former Kansas lawmaker tends to be belligerent -- his diplomatic chops.

Trump tweeted Thursday that "Mike Pompeo is outstanding. First in his class at West Point. A top student at Harvard Law School. A success at whatever he has done. We need the Senate to approve Mike ASAP. He will be a great Secretary of State!"

Sen. Tom Cotton, a Republican from Arkansas and close friend of Pompeo's, said on a Wednesday briefing call with reporters, "Now that he's actually sat down with Kim Jong Un, that is the best evidence imaginable that he is committed to diplomacy."

"It would, I believe, set back the preparations and the results of that upcoming summit for the Senate Democrats to oppose as a block Mike Pompeo's nomination to be secretary of state," Cotton said.

Many Democrats seemed positive or neutral about the trip.

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Sen. Mark Warner of Virginia, the ranking Democrat on the Senate Intelligence Committee, told CNN that Pompeo kept him "adequately briefed," telling him about the meeting after returning and before the news broke.

Moderate Democrats who are undecided on Pompeo's nomination say his secret trip is not a major concern as they decide whether to support him. "It might be a positive thing, actually," said Sen. Jon Tester, a Montana Democrat.

Sen. Heidi Heitkamp, a Democrat from North Dakota, announced Thursday that she would be backing Pompeo. Sen. Joe Manchin, a West Virginia Democrat, reiterated that he's "wide open" on the nomination. "We're still talking," he said.

Other moderate Democrats, as well as independent Sen. Angus King of Maine, declined to weigh in on the trip, saying they want to discuss it with Pompeo first.

Sen. Robert Menendez of New Jersey, the top Democrat on the Foreign Relations Committee, said Wednesday that the trip was one reason he was opposing Pompeo, as the nominee had been "less than forthcoming" in meetings with senators before the committee nomination hearing.

'The exact reverse'

Sen. Tim Kaine, a Virginia Democrat on the Foreign Relations Committee who also plans to oppose Pompeo's nomination, said he was "heartened by the news. I think dialogue doesn't have a downside, it has an upside."

Sen. Chris Murphy, a Democrat from Connecticut, said he had mixed feelings about Pompeo's trip. He had been worried the summit might be "for show ... that the President will then move to military options having given a try at diplomacy," Murphy said, and added that he was glad a high-level official was working on preparations.

But he said, "I have no idea why the CIA is pre-negotiating a summit between the American President and the North Korean leader. This should be the mission of the State Department."

Collins, of the Center for Strategic and International Studies, said the more prominent and highly unusual CIA role may pose problems. "That's very different from how things have happened in the past. Normally the State Department takes the lead," she said. "It just raises the stakes for this to be a failure."

The best-case scenario, Collins said, is if Trump and Kim get along fairly well personally and end the summit with a basic broad statement of principles -- for instance, the US supporting peace on the Korean Peninsula in exchange for Pyongyang's agreement to eventually dismantle its nuclear weapons program.

"And then they could work out the details through working level officials through a one- or two-year process -- the exact reverse of the way things usually work," Collins said.