Japan's status as a nonnuclear weapons state remains of ongoing interest to policy analysts and scholars of international relations. For some, Japanese nuclearization is a question not of whether but of when. This article reassesses the state of the evidence on the nuclearization of Japan. It finds that support in Japan for the development of an independent nuclear deterrent remains negligible. Evidence demonstrates that ministries and agencies with responsibility for foreign and security policy have sought to consolidate Japan's existing insurance policies against nuclear threats—multilateral regimes and the extension of the U.S. nuclear deterrent to Japan—rather than seeking an indigenous nuclear deterrent. The article also finds, however, that the door to independent nuclearization remains ajar. Policymakers have ensured that constitutional and other domestic legal hurdles do not significantly constrain Japan from developing an independent nuclear deterrent. Further, recent centralization of authority in the prime minister and Cabinet Office has increased the freedom of action of leaders, enabling them to overcome political opposition to changes in security policy to a degree not possible in the past. This suggests that Japan's future position toward nuclear weapons could be more easily altered than before, should leader preferences change.

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