A government report issued during the Clinton administration evaluated our chances in cas there was to be an invasion of Iraq. Seems that Bush, Cheney and Rumsfeld called the shots wrong even by standards established in the 1990's.
Posted on Boing Boing - read more here...
A secret US wargame called "Desert Crossing" produced during the Clinton era showed that an invasion and post-war presence in Iraq would require around 400,000 troops -- about three times the number of troops stationed there now. Even with those resources, according to simulation output, the mission could result in chaos.