This chapter examines Japanese perceptions of US primacy and the US-led order. It traces debates over American post-war leadership during early periods of uncertainty, noting both views against embracing US power and the more mainstream perspective that ongoing US leadership, and the primacy it is founded on, are essential for Japan’s own national and security interests. It argues that Japan’s contemporary policy responses are driven by this perception of the US role. It also argues that the US–Japan alliance has focused primarily on regional challenges, with Japan’s intention being to integrate American and Japanese security postures and interests as closely as possible to manage and deter regional threats, in particular China. The chapter further argues that Japanese governments have ‘securitized’ Japan’s Asia diplomacy. This chapter concludes with a discussion of the ‘Trump effect’ on Japan’s strategic thinking, that is, the serious challenge posed by Donald Trump’s unorthodox thinking and unpredictability to Japan’s ambition of maintaining a liberal, rules-based order in East Asia.