Some U.S. intelligence analysts and Iraq experts said they warned the Bush administration before the war about vanquishing Hussein's government without having anything to replace it. But officials said the concerns were either not heard or fell too low on the priority list of postwar planning.

Chalabi's influence, particularly with senior policymakers at the Pentagon, helped play down the prospects for trouble, some officials said. "They really did believe he is a Shiite leader," although he had been out of the country for 45 years, a U.S. official said. "They thought, 'We're set, we've got a Shiite -- check the box here.' "

Idiots.

The most common phrase that comes out of the US is...
U.S. officials said this week, it failed to fully appreciate

Yep either they just wanted a gung ho war and didn't bother with the rest, or they were incompetent, or they had bad intelligence (hey I just covered that one)