I would expect the Iranians to find a way out after establishing their 'leadership' credentials for the Muslim world. President Ahmadinejad is already on shaky ground with reformers, and the poor who voted for him are becoming disenchanted. He will need to turn inward soon and leave off the rhetoric. Conversely, any overt action from the US will cement his position as surely as any national leader, however incompetent, when a country is threatened. (I know it happened before, quite recently, just can't put my finger on where...)

I doubt if even the current US administration is dumb enough to engage Iran in any sort of hostilities. They are dumb enough to escalate this, however, so anything's possible - after all, they have pretty much guaranteed that Iran's old enemy Iraq will be an obedient puppet state -for the Iranians. (Shia controlled governments for the foreseeable, in case anyone is unsure).

There was a reason why previous US administrations installed Saddam Hussein as dictator and kept him there until he believed in his ability to get away with anything. He was a minority Sunni, and made war on Iran.