President Donald Trump is the wildcard when it comes to the potential summit between him and North Korean leader Kim Jong Un, according to a geopolitics expert.

“It is not clear what the calculus is with (Trump),” Lanhee Chen, a research fellow at Stanford’s Hoover Institution, told CNBC’s “Squawk Box” on Tuesday.

“We know that there are issues that trigger the president. But we don’t know exactly what the end game is,” he said, adding that the question of legacy could be very tempting to the president.

In comparison, North Korea’s Kim is seen to be the more predictable leader, Chen said.

“Kim Jong Un behaves in a certain way rationally,” the Stanford expert said. “We know (Chinese President Xi Jinping) is influential, domestic politics are influential, or maybe he wants an exit strategy. But with President Trump, it is more difficult to tell.”

With China working behind the scenes, Chen hinted that the potential summit and ongoing trade talks might instead be a smokescreen for more contentious issues that were brought up at the end of the Barack Obama’s presidency.

“There were no talks of strategic issues about the South China Sea, no talks on human rights,” said Chen. “More contentious issues in the U.S.-China relationship have fallen away in favor of this discussion about trade.”

As those issues take a back seat, many questions about U.S.-China engagement remain unresolved.

“They are playing a game of three dimensional chess,” Chen said of the leadership in Beijing. “The Chinese are talking about North Korea, but they are also talking about the influence of trade talks between the U.S. and North Korea.”