The United States has an extensive global network of security partnerships, the most important of which are in East Asia and Europe. U.S. allies in both regions are under increasing pressure from China and Russia, while President Trump’s contemptuous attitude toward them incites additional uncertainty about the reliability of the U.S. security umbrella. In particular, East Asian allies are anxious about Trump’s fluctuating relationship with North Korea’s Kim Jong-un, and are waiting to see the impact of Kim’s nuclear capability on U.S. military activity in the Korean Peninsula. Given recent concerns voiced by U.S. allies, it is crucial to evaluate the circumstantial similarities and differences between U.S. trans-Pacific and trans-Atlantic alliances in order to assess the overarching implications for the U.S. military alliance network going forward.