Very unlikely. Iran has the biggest military in the region in terms of active troop numbers (they are ranked 8th in the whole world), on top of that, the Basij is a paramilitary group that's estimated to be 3-5 million combat ready. Iran is also technologically fairly advanced, with its own arms industry, Chinese and Russian supplies, in the region it is only behind Israel and Saudi Arabia. General John Abizaid chief of United States Central Command for the Middle East region regard Iran as having the most powerful military (after Israel) in the region. A ground invasion would immediatly result in tens of thousands if not hundreds of thousands of US casualties. No politician with a brain will get in a direct military confrontation with Iran. The sabre rattling is more aimed at the US domestic constituencies and Israel than actually for Iran.
Iraq's military was (going off of memory) like the 5th largest in the world pre-Desert Storm. They didn't stand a chance and we had hardly any casualties. Iran would be the same. They have nothing, nothing, that could touch us. The only thing that would make a difference is if Iran got nukes, then we simply wouldn't attack them at all. I think we'd be about where we are now. The reason for this is we are spread too thin. I don't think we could sustain a 3rd front and I think McCain would understand that.