It is an item of faith for many Japanese – and many Japan watchers – that their country will never build or acquire nuclear weapons. Japan’s nonnuclear status, a product of both the searing experience of August 1945 and a calculation of the strategic value of nuclear weapons, has been a pillar of the nation’s postwar political identity. Recent developments could force Japan to reconsider the nuclear option, however. The U.S must step up, engage Japanese decision-makers in a serious discussion of their security concerns and work to allay them. Failure to do so could push Tokyo over the nuclear brink.