This has crossed my mind on a number of occasions. Clarke and Tenet, the two men who should have provided a smooth transition on the counterterrorism front and everything from 9-11 to Iraq can be boiled down to intelligence failures.
Problem is that on a gut-level I think Tenet was a stand up guy. He may either be the best actor in history or the job may have been too much for him. Clarke on the other hand is a puke.
I don't think Tenet ever got the full picture of what was coming. Don't forget Gorelick put up a wall that hampered many investigations. It wasn't until after 9/11 that we have been able to connect the dots.