When visiting htt://www.pollingreport.com , I found these two graphs, one describing the curve on whether or not voters believed that the U.S. had made the right decision on invading Iraq and the other their approval and disapproval of Bush.
What struck me immediately was how the curves were virtually identical showing how closely they were related; IOW, there seems to be a direct relationship between the public's perception on the Iraq issue and Bush's approval rating and a similar direct relationwhip between disapproval of the Iraq war and disapproval of Bush.
My conclusion is that he lives and dies politically on the public climate regarding the invasion. Below are the two graphs: