Just days before President Donald Trump will be face-to-face again with North Korean leader Kim Jong Un, the two sides remain divided on one of the biggest issues at the heart of their second summit.

Among the many unresolved issues as Trump and Kim prepare for another meeting Wednesday and Thursday in Hanoi, Vietnam is a common definition of what “denuclearization” would mean for the reclusive Asian country. A senior Trump administration official told reporters on a call Thursday morning that one of the top agenda items for the leaders’ second meeting is trying to agree to a “shared understanding of what denuclearization is.”

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“It is ultimately about the denuclearization of North Korea,” the senior official said. “That is what was agreed to [in their first summit last June]. That is the overriding goal that the president is seeking to achieve with this summit. … Eventually, we are going to need a full declaration in order to complete the process of denuclearization.”

The senior official described the June summit in Singapore as Trump and Kim “really, in some respects, breaking the ice.” But this time, both sides plan for the duo to “talk in more depth about the kind of future that North Korea could enjoy if it follows through on its commitment to final and full denuclearization.”

But Kim and his top lieutenants have not yet made it clear to their American counterparts that they define denuclearization as “final and full.”

The dispute over just how much of its nuclear and missile programs Pyongyang would give up in return for things like major sanctions relief likely will not be decided next week, Trump and his top national security aides have made clear in recent weeks. 

“I have no pressing time schedule,” Trump told reporters Tuesday. But he again made clear he would “like to see, ultimately, [the] denuclearization of North Korea.”

Like the commander in chief, the senior official on Thursday sought to tamp down expectations for the high-profile meeting, saying the White House hopes the two-day meeting will produce agreement on “an ongoing process of give-and-take.”

Trump’s public schedules this week have not included any meetings or other prep work for the second meeting with Kim. But the senior official described him as “doing everything necessary to be fully prepared.”

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The White House this week said Trump has had phone conversations with allies in the region — something GOP and Democratic lawmakers say will need to continue if he hopes to eventually reach a deal with Kim.

“Adept and agile diplomacy is critically needed on the Korean Peninsula,” Senate Foreign Relations ranking member Robert Menendez, D-N.J., said in a Feb. 12 statement. “The United States must continue to support and bolster our engagement across the region, and work with Japan and [South] Korea to build a forward-looking partnership for the 21st century.”

One House Democratic source said members will be pressing the president before he departs early next week to secure a firm commitment from Kim on returning the remains of U.S. troops killed there during the Korean war. The senior official told reporters that matter will be on the agenda next week.

With unresolved matters like that key definition remaining, the senior Trump official contended there is no plan to strike a deal for the sake of doing so.

The North must agree to a deal that meets “the international standard on how to go about addressing the issue of the elimination of weapons of mass destruction in a country like North Korea” the official said. “Nothing will be agreed to until everything is agreed to.