Deterring the Undeterrable

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Two ways: Begin by making the retaliatory threat in response to Iranian nuclear aggression so unmistakable and so overwhelming that the non-millenarians in leadership would stay the hand or even remove those taking their country to the point of extinction.

But there is an adjunct to deterrence: missile defense. Against a huge Soviet arsenal, this was useless. Against small powers with small arsenals, i.e., North Korea and Iran, it becomes extremely effective in conjunction with deterrence.

For the sake of argument, imagine a two-layered anti-missile system in which each layer is imperfect, with, say, a 90 percent shoot-down accuracy. That means one in 100 missiles gets through both layers. That infinitely strengthens deterrence by radically degrading the possibility of a successful first strike. Even Mahmoud Ahmadinejad might refrain from launching an arsenal of, say, 20 nukes if his scientific advisers showed him that there was only an 18.2 percent chance of any getting through-- and a 100 percent chance that a retaliatory counterattack of hundreds of Israeli (and/or American) nukes would reduce the world's first Islamic republic to a cinder.

Of course, one can get around missile defense by using terrorists. But anything short of a hermetically secret, perfectly executed, multiple-site attack would cause terrible, but not existential, destruction. The retaliatory destruction, on the other hand, would be existential.

We are, of course, dealing here with probabilities. Total safety comes only from regime change. During the Cold War, we worried about Soviet nukes, but never French or British nukes. Weapons don't kill people; people kill people. Regime change will surely come to both North Korea and Iran. That is the ultimate salvation.

But between now and then lies danger. How to safely navigate the interval? Deterrence plus missile defense renders a first strike so unlikely to succeed and yet so certain to bring on self-destruction that it might -- just might -- get us through from the day the rogues go nuclear to the day they are deposed.

We have entered the post-nonproliferation age. It's time to take our heads out of the sand and deal with it.

letters@charleskrauthammer.com