It is impossible to say, and a little unfair to try to imagine (not that I’m knocking your question or anything because it’s a valid one).  It would have definitely made it a lot more difficult for President Bush and his Administration to invade Iraq, and I think the Bush Presidency would be better-remembered if there had been no Iraq War.  With that said, it’s just so difficult to envision the Bush Administration without 9/11 that this question is impossible to answer.