The Trade Center itself held - and holds - a special place, I think, in the hearts and minds of people in law enforcement - the fact that it did not fall in 1993. Ramzi Yousef's goal was to topple the Twin Towers into each other so that more people died than had died at Hiroshima.

In terms of the breadth of the threat of Al Qaeda itself - it's not the only terrorist organization, and it works with others as cells around the world in at least 60 countries. You potentially are talking about tens of thousands of followers who can be conscripted into service to carry out a terrorist plot.

The 1993 Trade Center bombing was obviously frightening. It could have been much worse than it was.

I started my career in the private sector and then became U.S. attorney. I think I was a stronger U.S. attorney, and I frankly think I am a stronger Chair of the SEC, because of that experience.