and not because we've agreed to do so, and not because protecting ourselves might upset the Europeans, but because it is in our own unilateral self-interest. Specifically, it is important to be vulnerable to a "second strike"—that is, a retaliatory strike by an arsenal crippled by your potential "first strike." Why? Because you don't want anybody with nukes pointed at you to think they have to use 'em or lose 'em. As long as they can rain cataclysmic damage on us by striking second, they have no more incentive than we do to strike first."