An exporter of terrorism cannot get the bomb. We have every reason to try and keep a regime that has promised to wipe a nation off the map from obtaining a tool to do just that. Only responding after we lose a city or one of our allies is gone is not an option. We could deter the Soviets with MAD mutually assurred destruction because they could see the folly of a nuclear exchange. That doesn't exist for a suicidal martyrdom oriented radical religious regime. Waiting to count the bodies after a nuclear terrorist attack might fit the just war scenario, but it also fits the stupidity scenario. If our intelligence detects an immenent launch against Israel our ally, or we get intelligence of 10 American cities being targeted with dirty bombs or worse, there likely won't be time to convene a session of congress and get a declaration of war vote done. In my mind a serious credible threat is enough to act on. I don't want us to have to lose an entire city in order to respond. People hellbent on carrying out death on a mass scale would have no natural deterrence with setting dirty bombs in our cities. Deterrence has always been a big tool in our belt. It won't work with this nutty regime who believe that a major catastrophe will inspire thei Messiah (the Mahdi) to appear. If it was Obama staring down Putin in a showdown, a whole different story. It's only the Iranian regime, not the Iranian people. We have no reason to go in and target their citizens pre-emptively. The Israelis can handle the Iranians, but the ensuing chaos will be regional if not worldwide. And the Israeli's won't wait until they see a mushroom cloud rising over Tel Aviv to take action, nor should we or the world expect them to wait until a mushroom cloud is rising over Tel Aviv. They've already taken care of Iraq's nuclear facility at Osirik in the 80's, and Syria in 2007. They can do the same with Iran's but it will be much harder because the facilities are wider spread and hardened in underground bunkers, but THEY will get the job done with or without our help in the way of intelligence, equipment, or whatever, and the world should thank them, but we all know that won't be the case. We will probably help covertly and then apologize to the world for our brutish allies.