Trump-Kim summit: What it would take to move forward

WATCH LIVE MONDAY: You can watch livestreaming coverage of the North Korea Summit Monday starting at 7 p.m. ET on ABCNews.com or on the ABC News app available on the Apple App Store, Google Play Store, Apple TV App Store, Amazon Fire TV and Roku Channel Store.

The once uninmaginable summit between President Donald Trump and North Korea's Kim Jong Un is set to take place early Tuesday in Singapore, but hard questions remain about what might emerge from their historic meeting.

What are the possible outcomes that could satisfy the U.S. goal: that North Korea completely end its nuclear weapons program?

Longtime experts on North Korea bring a healthy dose of skepticism, concerned the summit is mostly about optics and will likely not produce substantive agreements.

Regardless, there is consensus the current environment that enabled the summit is preferable to the hot rhetoric of the past year that heightened chances of possible military conflict.

"We are in a better place than we were," said Michael Green a former National Security Council staffer who dealt with North Korean issues under the Bush administration and is now at the Center for Strategic and International Studies (CSIS). "This summit, whatever happens, is better than where we were before the Pyeongchang Olympics when we were talking about war."

Here's a look at what the Trump-Kim summit could produce – and what comes next.

Best case scenario

While there will likely be smiles and handshakes creating the impression of a successful summit, it's what happens behind closed doors that will be the true markers of any progress.

Trump and Kim are scheduled to meet privately on Tuesday in a 45 minute one-on-one meeting where only their interpreters will be present. They will later be joined by their senior advisers for a second round of meetings to be followed by a working lunch.

But serious talks between the two sides have been going on for more than a week at the Demilitarized Zone (DMZ) between North Korea and South Korea. Separate from the talks in Singapore, where negotiating teams dealt with the logistics of the summit, the DMZ meetings focused on the substance that will lead the way forward. And on the eve of the summit, the negotiating teams that met at the DMZ continued their talks in Singapore.

What's the likeliest outcome from a Trump summit?

"Some kind of framework, some kind of promises for promises document where North Korea makes certain pledges to take steps with respect to its nuclear program and the United States makes pledges in return," believes Jake Sullivan, who was former Vice President Biden's top national security aide, and is now a co-chair of National Security Action.

That framework will likely include a broad North Korean commitment to denuclearize and a peace statement that could lead to an eventual peace treaty.

But analysts place little stock in a North Korean commitment to denuclearize, commitments it made but reneged on, in previous nuclear agreements worked out with the Clinton administration in the 1990s and the Bush administration a decade later.

They believe a true indicator of whether a commitment to denuclearize is real would be for North Korea to actually list all of its nuclear and missile facilities.

Wendy Sherman, a former under secretary of state for political affairs, who negotiated the nuclear agreement with North Korea under the Clinton administration, believes there are two questions that, if answered, will be key to a successful deal.

"Where are North Korea's nuclear weapons?" and "Where are North Korea's ballistic missiles?"

"You can’t begin negotiating denuclearization if you don’t know what they have," said Green. "And they’ve never, ever, in all these agreements produced that, even though they were supposed to."

But since no one really knows the extent of North Korea's nuclear and missile programs a North Korean declaration of assets would likely be seen as incomplete. The "best I can expect is a partial declaration," believes Sue Mi Terry, a former CIA analyst now at CSIS. Beyond the nuclear threat, North Korea's missile program is of special concern to nearby South Korea and Japan.

And with skepticism that North Korea will ever truly do away with its nuclear weapons program, the best outcome might be to just accept some kind of a reduction in North Korea's threat capabilities.

For Green, that could mean that North Korea once again shuts down its plutonium reactor in Yongbyon or possibly agrees to a reduction in the 60 nuclear warheads it is believed to possess.

Even if there is no agreement to work out a peace treaty, Terry believes it's possible that both countries could open liaison offices to improve what has until recently been a non-existent diplomatic relationship.

What happens next?

If the Trump-Kim summit goes well, it could lead to additional meetings between American and North Korean negotiators that could result in concrete steps for how North Korea would denuclearize.

As this "middle of the road" scenario of extended talks plays out, North Korea would continue with its unilateral freeze on nuclear and ballistic missile tests.

For Victor Cha, a key indicator of whether the talks are serious will be if they are kept at the secretary of state level. "A Pompeo level that will meet frequently to implement on a timeline, the mandates, the declarations that these two leaders have made?" said Cha who was once the Trump administration's nominee to be the U.S. ambassador.

How long those talks take to reach an agreement could depend on whether President Trump sets an end date for extended talks.

And even if there is an agreement in the long term, it's possible that North Korea could restart its programs under a future American administration, as it did with the Clinton and Bush agreements.

"I think this middle path, if we end up with it, ends up with another president – or maybe this president again, dealing with a much more dangerous North Korea that escalates and creates a crisis again," says Green. "That’s the problem with the middle scenario."

Worst case scenario

If the summit fails, President Trump has said that the "maximum pressure" campaign of international economic sanctions against North Korea would continue.

But it's possible that the effort that brought North Korea to the negotiating table in the first place would continue to be effective, especially if China's commitment to the plan wavers.

"We’re already hearing reports that China is loosening its implementation of sanctions," said Terry. "And it’s going to be really hard to keep up this maximum pressure after the summit in this environment."

The lead-up to the summit has also created a change in the international landscape because of Kim Jong Un's new diplomatic outreach to Russia, China and South Korea.

The North Korean leader is no longer as isolated on the world stage as he was before, and there is always the possibility that he could seek a unilateral agreement with South Korea.

And if North Korea continues with its unilateral freeze on missile and nuclear tests, the U.S. talk of a pre-emptive military strike also loses its urgency.

"Kim Jong Un is very shrewd, he’s very smart. I think he’s been playing this very well," said Terry. "I think they’re pretty much set for a while."

"I can’t imagine that Kim Jong-un has any incentive to truly give it all up, particularly where verification is going to be so difficult to achieve," said Terry.

Another risk lies in overselling any progress made at the summit as a broad success.

“Progress is one thing, declaring success is another because a premature declaration of success would be taken as a green light by some of the key countries, particularly China, to go back to a business as usual approach with North Korea which of course would erode our leverage over the regime” warned Sullivan.