Juan Cole notes that Iraq could also disrupt sanctions against Iran:
American and Western discussions of what to do about Iran almost completely ignore Iraq. But no economic sanctions can effectively be placed on Iran without Iraqi support. A gasoline embargo would fail completely if Iraqis smuggled gasoline to Iran (which they certainly would, both for economic and religious reasons). Jalal Talabani, the president of Iraq, said Saturday that new sanctions on Iran "would not work" and that Iraq would never allow its airspace to be used for an aggressive attack on Iran "by any country" (he's looking at you, Israel and US). Somehow I don't think this is what Bush was going for when he invaded Iraq.
The Dish 