The Trump administration might view an annual negotiation as “leverage to increase Seoul’s defense cost-sharing,” and it’s “quite possible” that the administration could call on South Korea to pay the full cost of maintaining U.S. troops in the country, said Moon Chung In, a foreign-policy adviser to South Korea’s president who told me he was speaking in his capacity as a professor at Yonsei University.

If the United States goes that route, Moon noted, the challenge will be for both countries to arrive at some common understanding of how to calculate Seoul’s contributions for the upkeep of U.S. forces in the country.

Moon said that if the Trump administration were to press South Korea for new ways to cover the costs of the alliance in the coming years, he hoped that these would not include salaries for American soldiers and expenses associated with their weapons and equipment, all of which are not currently governed by the SMA. “If that is the case, South Koreans are not likely to accommodate such [a] request, because American forces in South Korea would then be like mercenary [forces], not [an] alliance force,” he told me.

He added that he didn’t expect Trump to slash U.S. forces in South Korea as part of a deal reached during his next summit with Kim, as many Korea-watchers in Washington and Seoul fear. For evidence, Moon pointed to a recent interview in which the president said he had “no plans” to do so. (Granted, in that same interview, Trump inflated the number of American troops in the country, described their presence there as “expensive,” and mused that “maybe someday” he would take them out.) “I trust [Trump’s] words,” Moon said, “and therefore I do not worry about it.”

Read: The mystery at the heart of North Korea talks

North Korea’s leaders have not specifically called for a U.S. military drawdown as part of their nuclear negotiations with the Trump administration. But they’ve stated that they see U.S. forces in South Korea as an obstacle to peace, and that they define the “denuclearization of the Korean peninsula” as encompassing the U.S. withdrawing from the region all elements of its military presence that pose a nuclear threat to North Korea in order for Pyongyang to consider giving up its nuclear weapons.

Plenty of American presidents have modified the U.S. military presence in South Korea as geopolitical realities have shifted. As he sought to end the Vietnam War and reconcile with China, for example, Richard Nixon withdrew tens of thousands of U.S. troops and prodded Seoul to “assume more of the burden of its own defense.” George H. W. Bush removed U.S. tactical nuclear weapons from South Korean territory at the end of the Cold War. His son diverted a combat brigade from South Korea to Iraq.