Even if Iran acquires a nuke, what can it do. It doesn't have the aircraft to make a strike. In fact WW3 is impossible. World Wars take place when two major superpowers go against each other and all other countries take sides. There are other superpowers, mainly China and Russia which are growing but there is no superpower capable of challenging the US at the moment. I think the US wants to jump on Iran, how it will do so I'm not so sure. As Matt said, it's unrealistic for the Pentagon.