Bamford opens by telling us that by 2008 NSA had become the most intrusive spy organization, secretly filtering millions of phone calls and e-mails/hour, programmed to listen for thousands of names and phone numbers. The watch list once contained 20 names - now its 500,000.
He then goes on to calmly describe how airport screening was easily evaded - true, a number of the 9/11 hijackers were given extra screening, but they had no explosives and their knives were less than 4" long. Pilots were ordered to place their aircraft on autopilot when the flights were taken over, and to move to the rear of the aircraft. The hijackers then turned off the airplanes' transponders, making them invisible to ground controllers.
Ironically, just as the NSA was becoming alarmed over the realization that some terrorists (and hijackers) were in the U.S., several of them were amidst NSA employees in local shops and on local highways near the agency.
Prior to 9/11, NSA head General Hayden had scaled back its intrusiveness out of fear of another Senator Church-type investigation. The NSA had been eavesdropping on them for years (without comprehension of what they were doing), and refused to pass information onto other agencies.
After 9/11 a secret program within the agency began, using an estimated 80-90 outside civilians that ignored FISA warrant requirements. Some objected, claiming that FISA requirements would not impede terrorist surveillance (eg. the warrant could be obtained as late as 72-hours after the fact, and were rarely refused), while Hayden pointed out that the forms and processing took time, and Cheney's Addington was outraged that under Bush II it had become a bit less than a rubber stamp.
Bamford goes on to reveal outcomes of these relaxed standards - considerable listening to private conversations between American military in Iraq and their families, etc. Also there is the strong possibility that those listening to conversations misjudge the intent (eg. An Iraqi says he's planning to deliver a load of melons - that may or may not be code for IEDs, and any erroneous decisions made on this limited information by those listening in (generally with limited Arabic fluency) bring harm or death to those involved.
Even more frustrating is that it is impossible to determine what is legal vs. illegal since NSA conduct is now governed by secret rules. Regardless, millions (possibly billions) are wasted as career CIA and NSA employees are hired by private contractors and placed back at their old jobs (often doing very little of potential value), computer systems between the CIA and National Counter-Terrorism Center are incompatable, and the entire intelligence system lacks accountability.
Frustrating NSA, on the other hand, was the fact that much international communications traffic to/from the U.S. is carried on fiber-optic cables - difficult/impossible to wiretap. This has led to NSA agreements with phone companies to divert cable traffic so that NSA could listen in.
All these conversations are recorded and stored in a new NSA facility in Texas. Readers are left wondering where this will all end and how much money is wasted.