Many studies of the Japanese prime minister in defense policy and politics have focused on the outstanding success of Prime Minister Koizumi Junichiro. These studies have noted the way Koizumi used the expanded resources of the kantei, bold public statements, and political theater to make significant changes to defense policy. However, just as important as exploring success in leadership is exploring failures. These failures can teach us about evolving political strategies and enduring aspects of international, regional, and domestic contexts. The prime ministership of Hatoyama Yukio (2009–2010) is an important case because it is the first time in recent history that a prime minister has challenged—however subtle that challenge may have been—the primacy of the U.S.-Japan Security Treaty. Hatoyama's prime ministership demonstrates the limitations of civilian internationalist approaches as a substitute for alliance maintenance with the United States, as well as the weaknesses of “consensus-based” and “muddle through” tactics in Japanese politics.