[Abraham]

I agree with Hitman that the US could take on Iran while continuing it's presence in Iraq, but I think it would take a high price, a price the US currently is not willing to pay.
That price would be:
1. political: an attack upon Iran without the solid backing of the Security Council (and even with) would do political damage to the image of the US;
2. military: it would take a lot of extra men, it would drain the National Guard and it would cost enourmous amounts of weapons and equipment (munitions);
3. humanitairy: it is clear that a lot of human suffering would result.

I could imagine a moment i time that the US would react towards the Iranian nuclear threat, but that moment will be months if not years down the road. At this time there is not yet a 'clear and present danger'.
Talking about the possibility of military action is putting some pressure upon the regime, but the most important thing is to deal with Iran as a unified international community. That unification takes more and more shape, no doubt helped by the completely irresponsable remarks with regards of Israel by premier Mahmoud Ahmadinejad.