It is a delicate matter to defend deterrence, the doctrine that it is the very lethality of nuclear weapons that lessens the likelihood of their use sufficiently to make us safe. That the consciousness of that lethality in the corridors of power in Washington and Moscow has played an important role in the keeping of the peace since the advent of the nuclear age is beyond doubting, as is the unwisdom of tampering with that consciousness, of accepting theories or technologies that will diminish the terror with which the prospect of nuclear war has been traditionally regarded and make nuclear weapons in any way less inhibiting to use. Still, if it is possible to underestimate the contribution that nuclear weapons make to the prevention of nuclear war, it is possible to overestimate it, too.
The essential fragility of deterrence must never be forgotten. Its central irony, that what may destroy us may be relied upon to deliver us, really is intolerable. That is the basis in reality for the criticism of deterrence from both the right and the left, for Ronald Reagan’s dream of ballistic missile defenses and for the peace movement’s dream of nuclear disarmament. Many of their arguments, to be sure, originate in moral, ideological and strategic assumptions that may be refuted. Against a great many alternatives, deterrence may be defended without apology. But there is at least one criticism of deterrence that may not be refuted: it may fail.
The failure of deterrence is a plain possibility. It does not require any form of scientific or strategic expertise to see it. Deterrence is a wager upon a broad variety of technological, military, political and diplomatic arrangements, any of which may collapse in a crisis; but at bottom it is a wager upon the human heart.