Jeffrey Lewis is director of the East Asia Nonproliferation Program at the James Martin Center for Nonproliferation Studies.

...If you know one thing about nuclear weapons, it is probably the eminently sensible moral from the movie WarGames: Regarding thermonuclear war, "the only winning move is not to play." Well, that's Hollywood. As recently declassified documents on the Carter administration's nuclear strategy make clear, the illusion of the winning move has been a reliable part of U.S. thinking about nuclear weapons. As long as the United States holds out the prospect of fighting and winning a nuclear war against China, the dialogue is going nowhere....

Some policymakers sought to impose some sort of limitations on the nuclear arms race, which seemed to be spiraling out of control by the early 1960s. In 1963, then-Secretary of Defense Robert McNamara championed a thought experiment to size U.S. nuclear forces. Imagine the United States has a force of 1-megaton nuclear bombs that we begin dropping on the Soviet Union, starting with Moscow. (Of course the United States did not have a force of uniform 1-megaton bombs, nor do we target cities. This was a thought experiment.) McNamara's Whiz Kids observed that the damage to the Soviet Union started to level off around the 400th bomb. McNamara didn't know whether 400 1-megaton bombs would deter another Joseph Stalin, but it was damn clear that if 400 didn't do the trick, flattening Perm with number 401 was a fool's errand.

The resulting policy was called "assured destruction" -- the idea that once the United States had a survivable force capable of about 400 equivalent megatons that could kill much of the Soviet Union's population and destroy its industry, there wasn't much point in making the rubble bounce. Say what you will about the tenets of assured destruction -- at least it was a ceiling.

Kahn and others did not like "assured destruction" because it did not hold out the possibility of prevailing in a nuclear war with the Soviet Union, something they believed was possible with bomb shelters, missile defenses, and hard hearts. (Decades later one proponent of victory summarized the argument by saying, "If there are enough shovels to go around, everyone will make it.") They went after assured destruction....