If you ask me,

(and nobody has, but I'll tell you anyway) the reason for our intelligence failures and our inability to prevent 9/11 is due to two factors:

1. Bureaucracy -- There apparently were warnings and clues that should have come together, but because of office politics and the slow process of reviewing and passing reports up the chain, and the refusal of different agencies to share information, these never got to a point where anybody could make a decision to do something about them.

There is also institutional inertia in any bureaucracy which rewards people for not doing things more than doing anything risky. Only after a calamity do heads roll and the obscure people who tried to do something get recognized. If 9/11 had been prevented, would we have heard about it? Would anybody have been rewarded? I doubt it.

2. Politics -- I've often thought about what the response would have been if the administration had started implementing more security at airports prior to 9/11. I think it's pretty obvious that there would have been complaints from airlines and passengers and criticism in the media and from Democrats charging paranoia and racism. If we had sought approval to move against Afghanistan to topple the Taliban and round up terrorists, the left would have gone nuts, the "international community" would have accused us of war crimes and the Congress would probably have voted against it. The media are about as rational these days as Al Qaeda itself, and would have been more so then.

This silly 9/11 Commission and its hearings are another aspect of the political jackassery that follows any event. It was the Senate hearings in the 1970s chaired by Frank Church that helped neuter the CIA and made it afraid of its shadow, which is one of the reasons that we had no human intelligence on terrorist groups and in Muslim nations. I don't approve of the CIA doing things like toppling foreign governments without the approval of the President, but it sure shouldn't have to be subjected to this kind of meddling by Congress either.