At present, the United States has approximately 28,500 troops positioned in South Korea to deter North Korea. In the past, South Korea has stressed the need to keep U.S. troops on the peninsula at the current level. In the end, South Korea paid around 8 percent more than the previous year, bucking Trump’s demands. But because Trump has a clear pattern of threatening South Korea on alliance issues, neither of these seems likely. Rather, the U.S. and South Korea probably have genuine differences and even grievances against each other, and this does not bode well for alliance modernization over at least the next three years.