Long before there is an air-war on Iran, there will be an economic embargo ... of gasoline. We could even do it unilaterally - use our navy to halt tankers, and use either airplanes or covert ground forces to cut the pipelines into Iran.
Consequence - the Iranian economy would crash within 30 days. And radio beamed into Iran would explain that this was aimed at the governing Mullahs rather than the people.
The Mullahs would then have to explain to the citizens of Iran why their policy to develop an atomic bomb actually benefits Iranian citizens.
It will then be the citizens of Iran who will have to make the decision - get rid of the mullahs, or side with them.
If the Mullahs ordered their Revolutionary Guard to attack the US positions in Iraq, they would remove the forces that are suppressing dissent, making a 2nd revolution possible ... in addition, the air war would start, starting with MOABs on their attack columns.
Recall Patton: "Give me the go-ahead, and I will have us at war with the Russians within 30 days, and make it look like it is their fault!"
We wouldn't drop MOABs on attack columns, it would be a whole lot of CBUs, anti-vehicle missiles and precision bombs.
Remember the "Highway of Death" in GW1?