HANOI — The outlines of a grand bargain between President Trump and North Korean leader Kim Jong Un are broadly in place. The question in Hanoi this week is whether the two men can close the deal.

June’s Singapore summit was widely criticized because Trump failed to secure concrete pledges from Kim to surrender his nuclear weapons, apart from a vaguely worded commitment to “work toward complete denuclearization of the Korean Peninsula.”

South Korean President Moon Jae-in, the strongest advocate of the engagement process, argued last month that it was time to move from abstract talk to concrete action when Trump meets with Kim again beginning Wednesday. But on Monday, he praised both men for traveling “on a path no one has taken before.” 

“President Trump is personally spearheading diplomacy toward North Korea with his bold determination and new diplomatic strategies in order not to repeat past failures,” Moon said in a statement. “If the upcoming summit produces results, now is the real beginning.”

On Sunday, the day before he left for Hanoi, Trump again boasted on Twitter of his “great relationship” with Kim and wrote that the two “expect a continuation of the progress made at first Summit in Singapore. Denuclearization?”

“Chairman Kim realizes, perhaps better than anyone else, that without nuclear weapons, his country could fast become one of the great economic powers anywhere in the World,” he added. “Because of its location and people (and him), it has more potential for rapid growth than any other nation!”

Speaking to CNN, Secretary of State Mike Pompeo expressed hope that the two leaders would take steps to realize what Kim promised in the last summit.

“He promised he’d denuclearize. We hope he’ll make a big step toward that in the week ahead,” Pompeo said.

His comments echoed those of a senior administration official who told reporters last week that the United States wants to “move forward with a number of initiatives that could specifically advance each of the four pillars of the Singapore joint statement.” 

Officials, diplomats and experts say it’s not hard to imagine what those initiatives might be. 

With regard to the first and second pillars, the opening of liaison offices in each other’s capitals would be a step toward transforming relations, and a declaration that the 1950-1953 Korean War is over would be a move toward permanent peace on the Korean Peninsula. And it should not be too challenging to make progress on the fourth pillar: the search for the remains of U.S. service members killed in the Korean War.

It is the third pillar, denuclearization, that really calls for tough talk in Hanoi — and is the area where Kim needs to prove that he means business.

“There are many things he could do to demonstrate his commitment to denuclearization,” Pompeo said Sunday. “I don’t want to get into the details of what’s being proposed, what the offers and counteroffers may be, but a real step, a demonstratable, verifiable step, is something that I know President Trump is very focused on achieving.”

In Seoul, lawmakers and officials have their eyes on the Yongbyon Nuclear Research Center, home to North Korea’s three nuclear reactors. 

The complex is the North’s only source of plutonium and also one — but not the only — source of the highly enriched uranium it uses to make nuclear weapons. 

Closing it permanently, in the presence of expert inspectors, would slow the country’s ability to produce more nuclear weapons, although it would leave its current nuclear and missile arsenal intact.

In return, North Korea would almost certainly demand sanctions relief. Pompeo said Sunday that “core economic sanctions” imposed by the U.N. Security Council must remain in place until the country completely denuclearizes but that other steps are possible.

“There are other things we could do — exchanges of people, lots of other ways that North Korea is sanctioned today that if we get a substantial step and move forward, we could certainly provide an outlet which would demonstrate our commitment to the process as well,” Pompeo told CNN’s Jake Tapper.

The United States has imposed some unilateral sanctions on North Korea over issues including its nuclear and missile programs, money laundering, support for terrorism and human rights abuses. Suspending some of those sanctions would require the president to certify to Congress that progress has been made in these areas, while others could be unwound by executive order, experts say.

But it is far from clear, they say, whether the American and North Korean negotiating teams have had enough time to reach a deal on the core issue — denuclearization — ahead of this hastily arranged summit or whether the two sides can even find common ground.

There are other risks, too: Some worry that Trump is so desperate for a deal, he may strike a bad one or that he simply isn’t interested enough in the details to secure a watertight agreement with Kim.

“Trump’s actually got to prepare for this meeting,” said Victor Cha at the Center for Strategic and International Studies. “He can’t wing it like he did last time.”

The United States will also be looking for Kim to spell out exactly what he means by denuclearization of the Korean Peninsula and whether his definition imposes any demands on U.S. forces stationed in South Korea or the region. 

The ideal would be a road map detailing corresponding steps toward denuclearization and sanctions relief, but experts said it is highly unlikely that such a document will be agreed to this week.

Last week, CNN reported that the United States and North Korea are seriously considering exchanging liaison officers, an incremental step toward building formal diplomatic relations. 

On Monday, Seoul’s presidential Blue House said the “possibility is open” that Trump and Kim will agree on how to declare an end to the Korean War this week. The war ended in an armistice rather than a peace treaty, signed by the United States, North Korea and China’s “People’s Volunteer Army,” a regular army force in all but name. 

South Korea says an end-of-war declaration could simply be signed by the United States and North Korea, although a formal peace treaty would eventually have to involve other countries.

“An end-of-war declaration between North Korea and the United States is sufficient on its own,” Blue House spokesman Kim Eui-keum told reporters Monday. “Our government would welcome any form the declaration might take, as the important part is the declaration’s role to smoothly bring on and accelerate denuclearization of North Korea.” 

But administration officials emphasize that the agreement should be seen as a package, with denuclearization at its core. 

“We are in the midst of negotiating on some issues and, as is often the case in these negotiations, nothing is agreed to until everything is agreed to,” said the official, who was not authorized to be identified.

Min Joo Kim contributed to this report.