The New York Times reports that the Department of Homeland Security's obsession with 9/11 has led to significant steps in preventing another such attack, including reinforcing aircraft cockpit doors and screening for weapons and bombs. But the steps have been reactive and not proactive.
Says Penrose Albright, a former DHS official:
What doesn’t exist yet is a risk management process. In the absence of coherent analysis, there’s no way to prevent the system from getting whipsawed. So it’s not surprising that we end up spending a lot of money fighting the last war and not addressing more modern threats.