Interesting point. While it is clear that Bush, in the first 8 months of an administration hamstrung by illegal obstructionism from the outgoing regime, was not responsible for the consequences of that derelict regime, still the political fact has always been:
The buck stops here. And if it happens on your watch, it's your problem. Except for Obama of course, that's the way it always works for other issues, so why not 9/11.
No doubt that Clinton bears most of the responsibility for 9/11. There was the 1993 WTC bombing, the bombing of our two embassies in East Africa in 1998, the attack against the USS Cole in 2000, and other incidents. OBL issued a fatwah in 1996 declaring war on the US. The signs were all there.
Once the attack took place, within hours, the FBI knew all the participants. They had been under the scrutiny of the agency. Because of the various stovepipes within the intelligence agencies, no one could put the dots together. We paid a terrible price.