The fiasco in Iraq was preventable. But Rumsfeld insisted it occur. Good for Newsweek for telling it like it is:
The administration was not just unlucky. It was almost willfully blind to the risks entailed in invading and occupying a large, traumatized and deeply riven Arab country. Rumsfeld, who pushed aside Rice and Secretary of State Colin Powell to take over even the planning for postwar Iraq, wanted a lean and mean force to get in and get out quickly. This was all well and good as long as American forces could turn over the job of running the country to an effective group of local Iraqis. But the planning for this was hamstrung by disputes over the postwar role of Iraqi exiles. When Iraq began to unravel, the administration—with little debate—lurched in the other direction. The White House installed Paul Bremer as a kind of grand pooh-bah over all of Iraq, but Rumsfeld refused to give him the forces he needed for a long occupation.
And Bush was so out of it and in denial that he simply acquiesced to the deranged intransigence of the real "decider," Dick Cheney.