They were clearly lying about the content of the Aug 6 PDB. When Ben-Viniste was questioning Condi, she said it was "historical" in nature, but she
also said:
And we checked on the issue of whether or not there was something going on with surveillance of buildings, and we were told, I believe, that the issue was the courthouse in which this might take place.
The 9/11 Commission report says (p 264),
Prior to 9/11, the FAA did present a CD-ROM to air carriers and airport authorities describing the increased threat to civil aviation.The presentation mentioned the possibility of suicide hijackings but said that “fortunately,we have no indication that any group is currently thinking in that direction.”
There are other things, but reading those two short parts convinced me that they must have been standing down in some manner.
I don't think they would have been OK with the World Trade Center towers going down - they are too business friendly to not prevent such a devastating attack, and a give and take evaluation of getting the country behind a war they thought needed to be fought may sound a reasonable calculation if it was a hijacking hostage crisis or a bombing of a courthouse perhaps killing a few people.
But I don't think they would have stood down to something as huge as what happened on 9/11 - aside from the sheer number of lives, they would have at least been prepared to shoot down the plane that hit the Pentagon.