Try this thought experiment: Would a nuclear Iran be so bad?
The prevailing view now is that a nuclear Iran cannot be safely contained. On this point both President Obama and Mitt Romney agree. They can hardly say otherwise; to even hint that a nuclear Iran is acceptable would undermine the efforts aimed at preventing that outcome. But I tend to think they mean it.
However, there are serious, thoughtful people who are willing to contemplate a nuclear Iran, kept in check by the time-tested assurance of retaliatory destruction. If the U.S. arsenal deterred the Soviet Union for decades of cold war and now keeps North Korea’s nukes in their silos, if India and Pakistan have kept each other in a nuclear stalemate, why would Iran not be similarly deterred by the certainty that using nuclear weapons would bring a hellish reprisal?