You say "delayed the inevitable" - I say the inevitable was a collapse of his regime, all by itself... neither of us can be proved right or wrong
There were three reasons - a gathering threat of WMD, links to terrorism (but not an involvement in 9/11) and "he's a bad man".
I, for one, would have considered it material if Bush believed (or continues to believe) that Saddam had a pivotal role in 9/11 ---> hence a statement like "the enemy attacked us" raises my eyebrows.