President Donald Trump will speak to North Korean Supreme Leader Kim Jong Un at a summit in Singapore Monday night to discuss North Korean denuclearization.

The summit will mark the first time a U.S. president has sat down to speak with a leader from North Korea, a prospect Trump said at the White House on June 7 “is going to work out very well.”

Trump said to reporters Saturday he has a “clear objective” for the summit and, as he left the Group of Seven summit in Canada, said the meeting would be a “one-time shot.”

This “clear objective” has been outlined by the Trump administration before, with the phrase “complete, verifiable and irreversible denuclearization.” As this phrase has been used extensively, it is often called CVID instead.

Richard Mansbach, political science professor at Iowa State, says verifying the denuclearization of North Korea could be a serious problem considering the geography and willingness of the Kim dynasty to cooperate.

“It is infinitely harder than in past deals to verify the denuclearization,” said Mansbach. “[Nuclear] facilities can be built into the Korean mountains, and, unlike the Iran Deal, North Korea already has nukes, [intercontinental ballistic missiles] and numerous areas to enrich uranium.”

Without the ability to verify, Mansbach says North Korea would take the opportunity to continue building nukes and ICBM’s, something the U.S. would see as a dealbreaker.

Denuclearization is another point of contention as the term is only loosely defined between the two nations.

President Trump says a denuclearization should include the north relinquishing all of their estimated 20 to 60 nuclear devices, the infrastructure that created the warheads, and all of their ballistic missiles that could be used to deliver payload across the Pacific.

Some, like Mansbach, say North Korea is not expected to give up their entire arsenal immediately. The decades it took to build their weapons and Kim’s distrust of Washington means it is more likely the deal will come in phases.

“Kim isn’t going to denuclearize immediately no matter what Trump thinks. They will likely do it over a 10 or 15 year period,” Mansbach said. “But they will want something in return.”

Economic aid, which the US, Japan, China and South Korea have agreed to, as well as limiting the ability of US oversight would be the baseline for North Korea, says Mansbach.

“They will likely want to keep their medium and short-range missile capabilities that hold, as hostage, US allies like Japan and South Korea,” Mansbach added.

The furthest request Mansbach sees North Korea going for would be removing U.S. naval, ground and air forces in South Korea and the region in exchange for denuclearization.

“I am not an optimist,” said Mansbach about the deal being successful after outlining the requests and issues from both sides.

Calling the summit a “mission of peace,” Trump said he would “be able to tell within a minute,” whether or not Kim is serious about the dealings on June 10 at the G-7 Summit.

“I feel that Kim Jong Un wants to do something great for his people, and he has that opportunity,” Trump said to reporters at the G-7 summit on June 9. “And it’s never going to be there again.”

Trump says, despite the hangups, he is confident a deal can be made.

“This is unknown territory in the truest sense,” Trump told reporters at the White House on June 7. “But I feel really confident. It’s never been done, it’s never been tested. So, we are going in with a really positive spirit.”

He says the economic assistance the US, Japan, China and South Korea have proposed could bring North Korea to terms with leaving their nukes immediately.

“I’d love to say it could happen in one deal, maybe it can,” Trump said in a statement to reporters Thursday at the White House. “They have to denuke. If they don’t denuclearize, that will not be acceptable. We cannot take sanctions off.”

“That’s why I feel positive, because it makes so much sense,” Trump said about North Korea meeting his terms.

Mansbach says the deal could fall apart due to Trump’s “erratic nature.”

“Our leader, who is vulgar, ignorant, thoughtless, illiterate, incompetent and is certainly the most dangerous single individual in this country I have seen since the days of Joe McCarthy, could ruin our relations at any moment,” said Mansbach.

Mansbach added that it was not a partisan attack, adding that he had voted for both democrats and republicans in the past.

The summit was called off following comments from US National Security advisor John Bolton, who said North Korea should take the Libya model of denuclearization, alluding to regime change in North Korea.

In 2003, Libya gave up the entirety of its nuclear capabilities but eight years later their leader, Muammar Gaddafi, was killed, and the regime was overthrown.

“The Libya comment gave North Korea a reason to keep their nukes,” said Mansbach. “If Un has a reason to think the US will remove him from power when he gives up his nukes, then he will keep them as a deterrent.”

The Trump administration pulled out of the summit on May 24 saying North Korea became hostile about the talks following Bolton’s remarks, but within days of cancelling the summit, Trump re-entered.

South Korean President Moon Jae-In played a large role in repairing relations between the two leaders by making a surprise trip to meet with Kim face to face.

Similar to Trump, Moon has spoken to reporters about the summit  and the prospect of complete denuclearization. His definition, however, is the most lenient of the three leaders.

Moon told reporters in Seoul on May 30 he wants to end the Korean war, which has been in a cease-fire since 1953 but never technically ended. Denuclearization, he said, can be figured out by Trump and Kim.

“It won’t be easy to narrow this gap and coordinate with each other, but our judgment is that it’s not impossible,” said Cho Myoung-gyon, Moon’s minister in charge of inter-Korean affairs to reporters about the likelihood of denuclearization. “Our assessment is that they will reach a compromise.”