But is that because of or in spite of the TSA?
When Napolitano said "the system worked" with regards to the underpants bomber... she was right... but not why she thinks.
Just as with the shoe bomber, both attacks were thwarted not by the TSA, not by attentive passengers... but because of limited options on the part of the terrorist.
In the old days, a terrorist would smuggle on to the plane almost anything as there was virtually no security. Whether it be DB Cooper or Pan Am Flight 103 the sky was the limit.
Know what happened? We started looking for such things. All of the sudden getting a traditional bomb, gun or knife onto the plane got a lot harder... so the bad guys would have to find other means. The problem though (as evidenced by both the shoe and underpants bomber) is that some of their alternatives are not as effective as they’d like... leading to an increased chance of failure.
Don’t get me wrong... the majority of what we face at the airport today is security theater... one upshot of which is we have (theoretically) increased the chances of finding a bomb/knife/gun carrier... forcing them to try to find more difficult ways.
Body scanners are not the answer... profiling and behavioral analysis is.
It’s no wonder El Al hasn’t been hijacked in in 40+ years. They take security seriously and don’t dink around with nonsense like forcing people to take off their shoes or (likely unhealthy) body scanners.