This combination of file photos shows US President Donald Trump, left, and DPRK leader Kim Jong-un. (EVAN VUCCI, KOREA SUMMIT PRESS POOL VIA AP)
SEOUL, Republic of Korea — When President Donald Trump and the Democratic People's Republic of Korea (DPRK) leader Kim Jong-un first met in Singapore last year, there was pomp, there was circumstance, but there wasn't much substance.
Those [concessions] would likely need to include jointly declaring an end of the 1950-53 Korean War, opening a liaison office in Pyongyang, allowing DPRK to restart some economic projects with ROK and possibly easing some sanctions on the DPRK
Before they meet again in Vietnam on Feb. 27-28, there's growing pressure that they forge a deal that puts them closer to ending the DPRK nuclear weapons threat.
READ MORE: Trump says to meet with Kim on Feb 27-28 in Vietnam
But what could that look like?
Kim may be willing to dismantle his main nuclear complex. The US may be willing to cough up concessions, maybe remove some sanctions. The question, however, is whether what's on offer will be enough for the other side.
Here's a look at what each side could be looking for as Trump and Kim try to settle a problem that has bedeviled generations of policymakers.
Destroying a nuke complex
The DPRK's Yongbyon (sometimes spelled Nyongbyon) nuclear complex, located about 100 kilometers north of Pyongyang, has facilities that produce both plutonium and uranium, two key ingredients in nuclear weapons. The DPRK's state media have called the complex of a reported 390 buildings "the heart of our nuclear program."
After a September meeting with Kim, the Republic of Korea (ROK)'s President Moon Jae-in told reporters that Kim promised to dismantle the complex if the United States takes unspecified corresponding steps. Stephen Biegun, the US special representative for DPRK, recently said that Kim also committed to the dismantlement and destruction of DPRK's plutonium and uranium enrichment facilities when he met visiting Secretary of State Mike Pompeo last October.
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Since fresh diplomatic efforts began last year, the the DPRK has suspended nuclear and missile tests and dismantled its nuclear testing site and parts of its long-range rocket launch facility. But destroying the Yonbgyon complex would be Kim's biggest disarmament step yet and would signal his resolve to move forward in negotiations with Trump.
There is worry among some, however, that the complex's destruction won't completely dispel widespread skepticism about DPRK denuclearization commitments. It would still have an estimated arsenal of as many as 70 nuclear weapons and more than 1,000 ballistic missiles. DPRK is also believed to be running multiple undisclosed uranium-enrichment facilities.
"We could call (Yongbyon's destruction) a half-deal or a small-deal," said Nam Sung-wook, a professor at Korea University and a former president of the Institute for National Security Strategy, a think tank affiliated with ROK's main spy agency. "It's really an incomplete denuclearization step" that matches past tactics meant to slow disarmament steps so it can win a series of concessions.
To get the DPRK to commit to destroying the Yongbyon complex, some experts say Trump needs to make important concessions.
Those would likely need to include jointly declaring an end of the 1950-53 Korean War, opening a liaison office in Pyongyang, allowing DPRK to restart some economic projects with ROK and possibly easing some sanctions on the DPRK.
Kim may most want sanctions relief to revive his country's dilapidated economy and bolster his family's dynastic rule.
"For North Korea, abandoning the Yongbyon complex is a fairly big (negotiating) card ... so the North will likely try to win some economic benefits," said Chon Hyun-joon, president of the Institute of Northeast Asia Peace Cooperation Studies in ROK.
North Korea is also referred to as the DPRK.
At the Singapore summit, Kim and Trump agreed to establish new relations between their countries and build a lasting peace on the Korean Peninsula. But they didn't elaborate on how to pursue those goals.
IN PHOTOS: Trump, Kim in historic Singapore summit
The DPRK has since complained about the lack of action by the United States, saying it already took disarmament steps, and returned American detainees and the remains of American war dead. The US for its part suspended some of its military drills with ROK, a concession to DPRK, which calls the exercises dress rehearsal for invasion.
Kim and Moon agreed at the first of their three summits in 2018 to settle an end-of-war declaration. Moon said last month it could ease mutual hostility between Washington and Pyongyang, and accelerate DPRK's denuclearization.
But some worry that a declaration ending the Korean War, which was stopped by an armistice and has yet to be replaced with a peace treaty, might provide DPRK with a stronger basis to call for the withdrawal of 28,500 US troops in ROK.
In his New Year's address, Kim also said he was ready to resume operations at a jointly run factory park in the DPRK's border town of Kaesong and restart ROK tours to the DPRK's Diamond Mountain resort. Those are two of the now-dormant inter-Korean projects that supplied badly needed foreign currency for the impoverished DPRK.
To make the Vietnam summit a blockbuster, Trump will likely need more than Yongbyon.
A bigger deal would see a detailed accounting of DPRK's nuclear assets, and possibly shipping some DPRK nuclear bombs or long-range missiles out of the country for disabling.
That would be costly. The DPRK would likely demand a drastic easing of sanctions and a resumption of exports of coal and other mineral resources.
A DPRK declaration of its nuclear program would provide invaluable information, if verified by US intelligence, to Washington and others. It would offer looks at hidden nuclear fuel facilities and missile deployments, which is why Pyongyang has been reluctant to provide it.
According to ROK and other assessments, Yongbyon alone is estimated to have 50 kilograms of weaponized plutonium, enough for six to 10 bombs, and a highly enriched uranium inventory of 250 to 500 kilograms (550 to 1,100 pounds), sufficient for 25 to 30 nuclear devices.
Undisclosed uranium enrichment facilities would up the stockpile.
Because of the difficulty involved, Trump may want to focus on the DPRK's long-range missiles, which could, when perfected, pose a direct threat to the US mainland. But such a partial deal would rattle many in ROK and Japan, which are well within striking distance of DPRK's short- and medium-range missiles.
If lower level officials can't lay the ground for a bigger deal ahead of the summit, the Kim-Trump meeting could be cancelled, said Lim Eul Chul, a professor at ROK's Kyungnam University who has advised the Moon government on DPRK-related policies.
HONG KONG NEWS