I don't think that military force is really practical against Iran, unless they attack us first. For one thing, it would shut down oil flowing from the Gulf, and that would mean $30 or $40 a gallon gasoline, not to mention a shortage of everything else as well. It would probably trigger a world wide depression. It would be a very bloody war that would be difficult to fight without oil.
Probably the only way the war could be fought as a practical matter would be with nuclear missiles.
Iran will not be preempted by the US. The military is not overextended yet, and attacking Iran just might do it.