Whatever happens the US won't actually invade Iran. They couldn't even if they wanted to. All they can do is send in some nukes and bust the place up a bit which would of course be Bush's dumbest move ever.
They have no proof Iran has a nuclear weapons program, and no proof Iran is supporting international terrorism.
By contrast, the US IS supporting terrorist groups by funding, supporting and training banned terrorist groups like MEK and Jundullah(An Al Qaeda affiliate!!!) to enter Iran and launch terrorist attacks on the Iranians in an effort to foment discord among the Iranians and force a regime change. The evidence of this is well documented. The leader of Jundullah was even given airtime on Voice Of America so he could boast about what his group has done!
My opinion, the US has completely lost the moral high ground. They have no right to accuse anyone else of supporting terrorism or torture, or building weapons of mass distruction, since they are guilty of it themselves.