The otherwise thoughtful Roger McKinney points out, in today's Reader Mail, that, "We couldn't stop the USSR, China, India, or Pakistan from getting the bomb, and we probably won't stop Iran. MAD prevented any of those countries from launching a missile, even though they were as crazy and paranoid as the Iranians." From that, he concludes that we needn't fear an Iranian nuclear attack. But he's entirely wrong.
MAD -- mutually assured destruction -- deterred the Soviets from attacking us because we had sufficient forces to mount a counter attack that would destroy them even though they were in the process of destroying us. It was predicated on a fact not present with Iran. If the Soviets attacked - by missile or aircraft - we would have known instantly and with certainty who the attacker was. With Iran, they would not do that for the same reasons.