As the Constitution enters its third century, its framework for the exercise of war powers is under siege. Presidential exercises of war powers to repel attacks, rescue lives, protect property, retaliate and threaten have posed the most persistent and visible challenge to that framework. But an equal theoretical challenge is posed by a power that the President has used only twice, the nuclear war power. Part I of this essay describes that challenge. Part II evaluates the constitutionality of the existing distribution of nuclear war powers. Part III identifies—but does not explore—alternatives.