Retired General William E. Odom offers about as pessimistic an assessment of the Iraq situation as you're going to find. Pay special attention to this paragraph in which he addresses the argument, "We must continue the war to prevent the terrible aftermath that will occur if our forces are withdrawn soon."
Reflect on the double-think of this formulation. We are now fighting to prevent what our invasion made inevitable! Undoubtedly we will leave a mess — the mess we created, which has become worse each year we have remained. Lawmakers gravely proclaim their opposition to the war, but in the next breath express fear that quitting it will leave a blood bath, a civil war, a terrorist haven, a "failed state," or some other horror. But this "aftermath" is already upon us; a prolonged U.S. occupation cannot prevent what already exists.
This is the Bush administration. They create a situation where no course of action will make things better, then lambaste their opponents for not putting forth a plan that will solve matters. Odom's piece, by the way, is entitled "Victory Is Not an Option."