After Donald Trump clinched the Republican Party’s presidential nomination, the possibility of the former U.S. president being returned to the White House has unnerved some countries, particularly allies troubled by his sometimes unpredictable and unilateral approach to foreign and defense policy.

This includes South Korea, which has heralded an unusually early start of defense cost-sharing talks with the United States — almost two years before the expiration of the current Special Measures Agreement (SMA). Renewed every two to six years since 1991, the SMAs reflect how the two sides split the bill for the upkeep of about 28,500 American troops stationed in South Korea.

The agreement on an early start of negotiations, which Tokyo will almost certainly be watching closely, appears to reflect concerns that Trump could once again drive a hard bargain on the issue of cost-sharing, which could potentially become a major bone of contention between the allies.