Best scenario would be for a multi-pronged, simultaneous hit on iran, syria, and the pakistani tribal areas. And not just military targets. In syria, all damascus power, transportation, and military infrastructure, in pakistan every village along the border followed by boots on the ground, in iran all manufacturing, refining, military, and hydro. Until they all cry "unconditional surrender."
But we won't do it, because our application of force isn't pre-emptive. Instead, there will be cruise missile and bombs on ied factories and several of the nuke sites in iran alone.
The application of force you suggest would not, in fact, be "pre-emptive" as I'm sure you will agree. Iran has been at war with the US since 1979. Force has been used by both sides, mainly covert by the Iranians. I agree, it is long past time that the US openly engage the enemy.