With what?
"An Act of War! On to Tehran!
With what?"
I wish I could dispute your answer. Unfortunately I can't.
Ever heard of the U.S. Military and airstrikes? Don't buy into the 'we're spread too thin' crap - we've got plenty of troops still stationed around the world, that we can call upon.
With what?
With airpower...at first. 6 months of intense shawk 'n awe. May never need to send troops...depending on how the Iranian opposition reacts.
I would approach Iran much as we approached Afganistan. Minimal ground forces, mostly spec ops designating targets and organizing resistance. We don't want to try and occupy Iran, too many things can go wrong.