Bush 41 was never a "diehard" Republican. He looked tired and out of gas in 1992 when Clinton beat him. Who can forget the scene in the debate when he looked at his watch?
Don't forget, that his foreign policy "team" was almost unanimously opposed to W.'s incursion into Iraq.
His whole life he's pretty much always been a northeastern Rockefeller Republican in most respects, and he clearly never really brought into the Reagan Revolution. He was fortunate to ride into office on the Great One's coattails, but it was pretty obvious that his heart was never really in the whole conservative movement. The one real accomplishment of his Presidency was the first Gulf War, and in retrospect he even managed to screw that one up.