Crossbow
Seeking Honesty and Sanity
Bush's problem was primarily his trust in Liz Cheney's dad, along with Rumsfeld and Wolfowitz. He's simply not all that bright.
While it is quite true that Bush Jr is quite stupid, however it is quite evident that Bush Jr has some very deep-seated motivations.
In this case, Bush Jr had always wanted to do something to show his father (who was the President, an Ambassador, a Director of the CIA, a war hero, a successful businessman, a Ivy League graduate, and so on) that his namesake son is a person of considerable worth.
And by settling the Iraq issue once and for all, Bush Jr could show his chops to both his father and his electorate.