WASHINGTON (AFP) - After a burst of hectic diplomacy, Donald Trump and Kim Jong Un's nuclear summit is on course to go ahead - but if it is to live up to the hype, both sides will need to make difficult concessions.
In what would be the first breakthrough in the fraught process, North Korea and the United States may sign a peace deal that could pave the way for a cautious thaw in ties.
"Can you believe that we're talking about the ending of the Korean War?" Trump asked rhetorically, marveling at his own diplomatic audacity.
The two countries have been technically at war for decades, even if their conflict was frozen by an armistice 65 years ago.
But what Washington is really seeking is the North's nuclear disarmament.
Pyongyang, however, has long insisted on becoming a respected nuclear state and - while it may have suspended nuclear and missile tests - surrendering its bombs is off the table.
So how can the circle be squared? How can the two parties arrive at what Washington says must be the "complete, verifiable and irreversible" denuclearisation of the Korean peninsula?
Many are skeptical.
"We'll know right away if it's a failure," Center for Strategic and International Studies analyst Boris Toucas told AFP.
"For example, if Kim won't give written guarantees on denuclearisation or if there's just a declaration of good intent without a roadmap."
The summit would be a challenge for the most seasoned diplomats and just last year neophyte statesman Trump was mocking Kim as "Little Rocket Man," while the young autocrat sneered at the "mentally deranged dotard."
MAN IN A HURRY
The stakes have been raised still further by the accelerated timeframe. Trump may have conceded there will be no grand deal at the first meeting, but he wants a win before his first term ends in 2021.
North Korean leaders have been seeking face-to-face talks with a sitting US president for a quarter of a century, but Trump only agreed to meet Kim in March and now seems to be in a hurry.
So much of a hurry, in fact, that many in Washington worry he will naively make concessions without securing the North Korean arsenal.
But the cynics were also cheered that Trump now publicly accepts that the meeting is probably only the start of the process, and some former officials think some progress can be made.
Ambassador Joseph Yun was the US special representative for North Korea until days before Trump accepted the summit invitation, and is a veteran of backchannel talks.
He said that if the summit is to count as a success, both sides will have to make rapid concessions to build trust before a longer process leading to eventual disarmament and normalization can begin.
"The basic proposition that the United States is trying to tell North Korea is: 'You are safer without nuclear weapons than with nuclear weapons,'" said Yun, now an advisor at the US Institute of Peace.
North Korean leaders have long assumed the opposite: Only with weapons can they secure the Kim dynasty's survival and become a respected nuclear power like India, at the diplomatic top table.
But certain security guarantees may convince Kim to follow the diplomatic path after the summit.
"One, I believe in this particular instance would require what I call an 'end of war declaration,' that the Korean War, which technically ended with an armistice in 1953, is over," Yun said.
"Then you would require to have that, in effect, a peace treaty negotiation. And then, of course, along with that you need diplomatic normalisation. So you can see it's a long drawn out process."
If the United States agrees to begin - as Trump appeared to suggest it might - peace talks to end the war and to open a diplomatic liaison office in Pyongyang, Kim might see the talks as useful.
Frank Aum, a former top advisor on North Korea to US defence secretaries and now also an expert at USIP, said Kim will have military demands.
For Pyongyang, "denuclearisation" means not just surrendering its own bombs, but banning US strategic assets like F-22 stealth fighters, B1 bombers and carrier battle groups from its region.
But what must Kim give up in return?
"North Korea is probably ready to say that at the end of the day that they are ready to completely denuclearise, but there will be a comma and a fine print," Yun said.
Trump, who prides himself as a dealmaker, will have to negotiate this fine print so that Kim cannot delay indefinitely while international economic and diplomatic sanctions start to fray.
Kim, Yun said, should immediately put into writing what he has already agreed to do: halt his provocative tests of long-range missiles and nuclear devices.
He should also allow international inspections of his declared nuclear sites such as Yongbyon and - crucially - reveal his other, secret sites to make clear the scale of the disarmament task.
Only then could US negotiators begin to judge whether the North Korean leader is serious about his eventual disarmament - and US intelligence reportedly does not believe he ever will be.
For Yun, Kim's seriousness and the relative success of Singapore talks will only be confirmed "if there are deliverables that are concrete and quick, and that is clearly what our side will be looking for."
Experts worry that North Korean foot-dragging, encouraged by a China and Russia that have warned against precipitating the process, could prove intolerable to the Trump administration.
"Clearly, North Korea is looking at a phased process. China and Russia also agree," Aum told reporters.
"The US, on the other hand, wants to have an accelerated process that provides many of the denuclearization processes up front and then South Korea is in the middle."
Siegfried Hecker of Stanford University, who once ran the US atomic lab in Los Alamos, has said that from a technical point of view alone, verifiable disarmament could take 15 years.
Yun and Aum said interim concessions from both sides could get the process started within a year, but if it collapses, Kim may be happy to cut his losses and enjoy a technical win.
"The summit itself is already an enormous concession from Trump. It gives Kim enormous legitimacy on the international and domestic plane, even if in the end it fails," Toucas told AFP.