Despite the White House’s dramatic Thursday evening announcement of President Trump’s decision to accept a meeting invitation from North Korean dictator Kim Jong Un, the historic summit between two feuding leaders is far from a certain occurrence.

White House officials have stressed that Trump will not sit down with Kim until Pyongyang meets a set of preconditions, but aides have declined to specify what those preconditions might entail.

And although White House press secretary Sarah Sanders argued Friday that Trump “is getting exactly what he wants” by securing a prospective meeting with Kim, she noted the encounter remains contingent on North Korea taking “concrete steps” toward denuclearization before the administration sets a date and location.

White House officials have highlighted the concessions North Korea made to earn Trump’s tentative agreement to attend the meeting, all while making no concessions to Pyongyang about U.S. military presence in the region or the American alliance with South Korea. North Korea has agreed to cease its nuclear and ballistic missile tests while its leaders negotiate with their South Korean counterparts, and the Kim regime has committed to denuclearizing at some point in the future.

Harry Kazianis, director of defense studies at the Center for the National Interest, said the summit between Kim and Trump is not guaranteed to materialize just because Trump accepted the invitation.

“I would say the chances are 50-50,” Kazianis said of the likelihood that the meeting occurs.

“The only way these men are going to get in the room is if they can essentially pre-negotiate what the outcome will be,” Kazianis said. “There has to be some kind of clear deliverable that both men could say they got a win from.”

Preconditions could include determining in advance the nature of the meeting, whether it is a “get to know you” discussion or simply a photo opportunity for the two leaders, Kazianis said. The terms could also be more substantive, such as a timeline for Pyongyang to discard its nuclear arsenal.

Trump said just days before announcing the Kim summit that a dialogue between Washington and Pyongyang would be “a great thing for the world.”

However, his entire administration did not appear to be lined up behind the idea of talks with the North Koreans heading into the unexpected announcement on Thursday of a summit.

Secretary of State Rex Tillerson said Friday he had spoken to Trump earlier that morning, but noted the president made the decision to accept Kim’s invitation on his own. Just hours before the White House announced Trump’s meeting with Kim, Tillerson said the U.S. was “a long ways from negotiations” with North Korea.

Speaking in Djibouti on Friday, Tillerson argued “people continue to struggle with the difference” between negotiations and “talks,” claiming the words denote different types of diplomatic encounters.

“My comments have been that we’re – the conditions are not right for negotiations, but we’ve been saying for some time we are open to talks,” Tillerson said.

“In terms of the decision to engage between President Trump and Kim Jong Un, that’s a decision the president took himself,” the secretary of state added. “I spoke to him very early this morning about that decision and we had a good conversation. This is something that he’s had on his mind for quite some time, so it was not a surprise in any way, because I think this has long been something.”

Sanders dismissed speculation on Friday that the president had cut Tillerson out of the loop on the Kim decision, noting Tillerson’s deputy had been present in Oval Office discussions about accepting the invitation.

The administration has said the talks with Kim will proceed with buy-in from the international community, most of which has joined Trump in imposing crippling sanctions against North Korea.

Trump spoke Friday with Chinese President Xi Jinping about the prospect of talks with Pyongyang. Xi encouraged Trump and the North Koreans to avoid taking any steps that could dash hopes for a meeting, according to Chinese state media.

Sanders noted Trump had spoken to several world leaders since accepting Kim’s request to meet in person, although she did not identify who specifically he had contacted. Many countries expressed optimism about the potential summit between Trump and Kim as a step toward peace on the Korean Peninsula.

“This is something that all of these countries have been working together on,” Sanders said.

Kazianis said war could break out with North Korea if the talks between Trump and Kim fall apart in the weeks ahead.

“It’s the ultimate Hail Mary, and if it goes bad, and it falls apart, we're back near the brink,” he said.