George Bush in an interview with the Wall Street Journal (subs. req'd; alt. free link) --
WSJ: Was there a moment in the war when you said we have to make a major change in the way we're doing things in Iraq?
GWB: Yes, there was.
WSJ: When was that?
GWB: Violence. It looked like it was uncontrollable. A young democracy is not going to survive if its capital city is in sectarian violence. I thought for example after the Samarra bombing that we were going to be fine. I thought the Shias had looked into the abyss of a civil war and pulled back. We thought they had, and they didn't.
This was information that he didn't think the voters needed to know before the election.