The ROK-Japan relationship seemingly found a floor after the downward spiral that marked the end of the Lee Myung-Bak presidency and the first three years of President Park Geun-hye. Seoul and Tokyo are now cooperating more closely together and with the United States to address the North Korean security threat. In particular, hard military cooperation has been enhanced as the three countries’ navies hold joint exercises and their diplomats have increased the tempo of meetings to better align policies. Fault lines and points of disagreement persist, however, in particular the fate of the December 2015 “comfort women” agreement. The election of Moon Jae-in in Seoul and Donald Trump in Washington could pump new centrifugal forces into these bilateral and trilateral relationships, however, erasing those gains. Strategists in both countries should be concerned about their country’s prospects in the middle- and long-term. In many ways, options will diminish and the best counter to those shrinking horizons is the forging of relationships with like-minded partners who share geopolitical concerns. Dealing with North Korea (or northern Korea post-unification) poses a special problem for Seoul. In either case, China will retain outsized influence over South Korean policymaking, and THAAD is illustrative of how Beijing will try to use that influence in an overbearing and heavy-handed manner. It makes much more sense for Seoul to attempt to use Japan as an offshore balancer to limit Chinese influence and overreach.