Ever since he met Kim Jong Un in Singapore last year, President Donald Trump has shown a tendency the North Korean leader is sure to try and exploit: making unexpected concessions in one-on-one meetings.

There was the December phone call with Turkey’s president, when Trump surprised his own aides — and prompted Defense Secretary Jim Mattis’s resignation — by suddenly agreeing to pull troops out of Syria. And last year’s joint press conference with Russian President Vladimir Putin, when Trump all but dismissed his own intelligence community’s findings on Russian hacking of the 2016 election.

Heading into next week’s summit with Kim in Hanoi, the president’s top advisers will seek to ensure no last-minute giveaways happen this time around. But for North Korea, the president’s habit of making concessions on the fly presents an opportunity that’s likely to lead negotiators from Pyongyang to disregard the president’s staff to focus on what he might offer.

“They do look to get President Trump in a room and see what they might get out of him,” said Christopher Hill, the North Korea negotiator under President George W. Bush. “If Singapore is any indication, the president seeks to want to negotiate everything himself.”

When the two leaders met last June in Singapore, Trump accepted a vaguely worded statement about “complete denuclearization of the Korean Peninsula.” In exchange, he had already given Kim a priceless public relations victory just by agreeing to talks. Trump also extended a suspension of major joint military exercises with South Korea, even adopting North Korea’s terminology on those drills — calling them “war games” and “provocative.”

Kim and his team seem to be betting on a repeat. A senior Trump administration official, who asked not to be identified discussing internal deliberations, said North Korean officials have so far given little away in their meetings with the top U.S. envoy for the talks, Stephen Biegun. The official said the fear is that Kim will make an offer to Trump that sounds good at the moment, inspiring the president to sacrifice something in return that goes too far.

Those fears have largely focused on the fate of about 30,000 U.S troops stationed in South Korea. Kim could seek to exploit Trump’s own professed distaste for overseas deployments to extract a commitment to withdraw some or all of them as part of a deal to secure a peace agreement.

The U.S. and South Korea recently concluded weeks of bruising negotiations that got President Moon Jae-in’s government to increase its payments for hosting American troops, but Trump and his team have indicated they want Seoul to do more.

“I could see Kim saying, ‘South Korea is reluctant to pay for the troops so why don’t you withdraw them?”’ said David Maxwell, a senior fellow at the Foundation for Defense of Democracies and a former special forces colonel in South Korea. “It’s most important we disabuse him of that notion that he can make a deal without the working-level foundation.”

Observers such as Maxwell point to a range of evidence to suggest this is North Korea’s strategy. They cite a refusal to meet with Biegun for months after he was named the lead U.S. negotiator in August 2018.

Biegun got his first formal meetings in January, and complex talks on an agreement from the summit got underway only recently, just a few weeks before Trump and Kim meet. And while the window to achieve anything of substance is short, that didn’t stop the president from agreeing to a second summit where pressure will be high to move beyond the vague agreements from Singapore.

Ever since his early real estate days, the president has believed he’s the best negotiator in any room, and the intimacy of a one-on-one chat is often where he thinks he can get the best deal. Trump has said he and Kim “fell in love” last year and that North Korea has enormous economic potential under Kim.

Secretary of State Michael Pompeo said Thursday in an interview with NBC’s “Today” show that the president and his team remain focused on the end goal of “complete denuclearization” of North Korea and that the main U.S. leverage, UN-backed sanctions, will remain in place until then.

This time may also be different because there’s more effort underway to reach a deal beforehand. Biegun flew to Hanoi on Feb. 19 to meet with his North Korean counterparts, and Pompeo will arrive in the city a day before Trump. Last time, Pompeo flew to Singapore with the president, and his negotiators were working out the summit declaration’s wording just hours before Trump and Kim were scheduled to met.

North Korea has shown a preference for Trump, with Pompeo facing a fraught trip to Pyongyang in July where North Korea issued a harsh statement after he left and then it canceled a meeting with him planned for November at the last minute. In December, North Korea’s official media accused the State Department of slander “out of sheer malice” and praised Trump for availing “himself of every possible occasion to state his willingness to improve DPRK-U.S. relations. ”

“I don’t want to get into the negotiations, what we might give up, what they might give up,” Pompeo said. But when it comes to sanctions, “we won’t release that pressure until such time as we’re confident that we’ve substantially reduced that risk,” he added.

More generally, the administration defends Trump’s negotiating style, underscoring that decades of negotiations at lower levels by previous Republican and Democratic administrations failed to produce lasting agreements.

“This is a top-down approach with the chairman and the president meeting directly and that allows for a breadth of action, frankly, that if successful could fundamentally transform relations between our two countries,” State Department spokesman Robert Palladino said this week.

‘Guardedly Optimistic’

Supporters of the president’s diplomacy argue that by agreeing to a second summit, Kim will also be under pressure from Pyongyang’s elite to show that negotiating with Trump has been worthwhile, even if sanctions remain. They also say that the delay in meeting Biegun may have nothing to do with the U.S. and be part of some internal power play within North Korea.

“I’m guardedly optimistic on the summit,” said Joseph DeTrani, former head of the National Nonproliferation Center, a part of the U.S. intelligence community. “There’s so much that could be put on the table that would include true substance.”

In a call with reporters on Thursday, two senior administration officials, who asked not to be identified discussing plans for the summit, confirmed that the event will include a one-on-one meeting between Trump and Kim. They ruled out the idea that the U.S. was prepared to discuss reducing troop levels.

That has done little to reassure critics of the president’s approach.

“We know who Donald trump is, we’ve seen two years of this, and we’ve seen where Kim and the North Koreans are trying to go,” said Laura Rosenberger, a senior fellow at the German Marshall Fund of the United States who advised President Barack Obama on North Korea policy. “The question is: How do we manage the risk, how do we walk away with the least bad outcome?”