Whether or not the upcoming U.S.-North Korea summit goes smoothly, Donald Trump has already scored an unequivocal win with the release of three Americans detainees.

And according to former diplomats and non-proliferation experts, Pyongyang's concession has put the onus on Washington to continue the positive brinkmanship that the isolated regime can take credit for initiating.

It's likely just as North Korean dictator Kim Jong-un intended, said Mintaro Oba, a former State Department official in the Obama administration who worked on North Korea policy.

"North Korea recognized that its sincerity would be called into question if it didn't release these detained U.S. citizens," Oba said.

"It allows North Korea to paint themselves as the drivers of progress and puts pressure on the U.S. to either reciprocate or not to disrupt the positive atmosphere."

Kim is known as a calculating ruler; it's safe to assume he expects a trade off, as in any diplomatic negotiation, Oba said.

North Korea has now set the stage for the summit, experts say, by meeting American preconditions to release the prisoners, stopping nuclear and long-range ballistic missile tests, and agreeing to discuss the prospect of denuclearization.

U.S.President Donald Trump meets the three Americans formerly held in North Korea upon their arrival at Joint Base Andrews, Maryland. (Jim Bourg/Reuters)

Releasing the three detainees allows Kim to portray himself as a "reasonable actor," according to defence analyst and retired Lt.-Col. Danny Davis.

The trio — Kim Dong-chul (accused of espionage), Tony Kim (accused of unspecified crimes to overthrow the government) and Kim Hak-song (accused of anti-state activities) — touched down at Andrews Air Force Base in Maryland early Thursday morning and were greeted by President Trump himself.

"It's a great deal for the United States; certainly it is for these men and their families," said Davis. "It also appears Kim is saying, 'Hey, look, I'm willing to take some first steps.'

"These are confidence-building measures to show he's sincere about this — either to make Trump think it, or make global public opinion think he's going to be reasonable in negotiations."

Win-win

At the same time, Kim hands Trump a political victory and frames the talks in a positive light — a sign Pyongyang wants this meeting to go well, said Davis.

"It's a chess move," he said. "But it's win-win."

Kim will do "whatever he can" to give himself the maximum advantage, Davis said. "Up until these negotiations, he had nothing to gain to just give something back, because we didn't ask for it."

North Korean Leader Kim Jong-un, left, prepares to shake hands with South Korean President Moon Jae-in during last month's Koreas summit. (Associated Press)

Trump tweeted Wednesday that the three released Americans would soon be reunited with their families and all seemed "to be in good health," allaying fears they might meet the same fate as Otto Warmbier, the imprisoned college student who was sent home to the U.S. last year in a coma.

Warmbier died less than a week later, having suffered brain damage.

This recent homecoming was "a goodwill gesture" ahead of the summit, the White House said in a statement. However, a North Korean official quoted by Reuters reportedly warned the Americans upon their release that they should "not make the same mistakes again."

'Low-hanging fruit'

But it'd be wrong to presume this undeniable boost for Trump means Kim is caving to diplomatic efforts, said Catherine Dill, a Washington-based nuclear nonproliferation and East Asian security expert, with the Middlebury Institute of International Studies at Monterey.

With complex issues on the table — and the U.S. intent on getting North Korea to ultimately move forward with an irreversible shuttering of its nuclear program — Kim chose "low-hanging fruit" to first offer the Trump administration, she said.

"It's a positive step but this doesn't surprise me," said Dill. "Releasing three prisoners is, in orders of magnitude, much easier than negotiating a verifiable denuclearization timeline."

North Korean Leader Kim Jong-un leaves the Peace House after a dinner at the last month's Koreas summit. By meeting with South Korea's Moon Jae-in and China's Xi Jinping, Kim may be trying to position himself as a statesman before meeting Trump, one expert says. (Korea Summit Press Pool/Getty Images)

And whether this outcome was the result of American pressure is hard to determine, Dill said, though she noted South Korean President Moon Jae-in had made a similar request for the release of six South Korean detainees during the Koreas summit last month.

"North Korea did not decide to comply with that request but chose to with this one. I'm not sure if that means they feel the U.S. needs more incentive to actually schedule this summit, or if they're taking the U.S. summit more seriously."

Either way, it's clearly part of North Korea's strategic calculus, Dill said.

She also said she hopes the U.S. and North Korea are entering into "classic diplomacy," given what little is known about how the State Department is functioning under the new leadership of Mike Pompeo.

Kim appears to be girding himself heading into these talks, Dill said, which have been set for June 12 in Singapore.

The highly anticipated meeting between Kim Jong Un and myself will take place in Singapore on June 12th. We will both try to make it a very special moment for World Peace! —@realDonaldTrump

Kim has already held a charm-offensive summit with Moon on the South Korean side, and has met twice with Chinese President Xi Jinping, taking what Dill called "an aggressive approach" by acting the part of a true statesman.

Skepticism still reigns

Releasing the three American detainees advances his mission to secure a summit that could be crucial for the North getting what it wants out of a possible deal: relief from biting sanctions that have prevented North Korea from achieving the economic modernization its leader craves.

While Lisa Collins, a fellow with the Korea Chair at the Center for Strategic and International Studies in Washington, doesn't believe human lives should ever be used as "pawns in any kind of political game," she said North Koreans have likely used detainees in the past as leverage to engage the United States.

And freeing the trio "doesn't absolve North Korea of the fact it's still a human rights-abusing country and still has hundreds of thousands of people detained at prison camps inside its own country," she said.

Harry Kazianis, director of defence studies at the conservative Center for the National Interest, also remains skeptical of any attempt to build trust.

In an op-ed arguing Kim is unlikely to relinquish his nuclear arsenal, Kazianis quoted a chilling passage from an interview he said he did with a defector four years ago:

"The Kim family not only killed my entire family, but they broke my soul into pieces that I will never be able to put back together. You don't talk to monsters like that — you fear them. You run from them. And you never trust them. Ever."