There's a lot of effort to figure out who is to blame for 9/11 these days, from the Clarke book to the 9/11 commission. If we want to know who's responsible, however, it's dangerous to blame Presidents and administrations but not the people they led. No president wants to go to war without a popular mandate, and before 9/11, it simply wasn't there. It's possible that Clinton could have built a mandate based on the previous attacks, but it would have been nearly impossible for Bush to make the case in the first 8 months he was in office. It wasn't until September 11th that the American people were ready to support a war.
I think debates which ignore the political realities are missing a large part of the equation.