Remember the “threat” environment on the morning of 11 September 2011. Al Qaeda was on the march, and it had been allowed to fester under Bill Clinton’s watch. We knew the group had a long-standing interest in some sort of “aviation spectacular,” but the possibility was down-played. And of course, the FBI famously rejected that memo from a field agent in Minneapolis, alerting her superiors about Arab men in local flight schools who had no interest in learning to land the planes they were piloting.
From an air defense standpoint, the traditional threat (from long-range Russian bombers) had essentially evaporated. TU-95 flights against Alaska, the west coast, Pacific Islands and the U.S. east coast occurred rarely, and there was often a gap of years between those missions, since the Russian military was essentially bankrupt.
Against that backdrop, the number of fighters on air defense alert was decreased and many were placed on a lower alert posture—including the removal of air-to-air missiles. Air defense of the CONUS became a lower-priority mission, with less training and fewer personnel.
And, making matters worse, there was little joint practice with the FAA; simply stated, no one believed the scenario that unfolded on 9-11 was possible, so everyone was completely unprepared for it. Watch the various documentaries that include radio traffic from the Northeast Air Defense Sector (NEADS), which was assigned to defend the airspace in which the attacks occurred. They were quickly overwhelmed, not just due to a lack of resources, but because they were in uncharted waters. No one had ever conceived—let alone practiced—for the events that unfolded on that September morning 15 years ago.
The first part of this statement is simply untrue.
Note the part about crashing one of the aircraft into CIA headquarters in Virginia.