The astonishing specter of September 11, 2001, jarred America and, indeed, all free nations, into accepting the previously unthinkable- the world's only remaining superpower is vulnerable to catastrophic attack and asymmetric warfare, even within its own borders. In a few short hours Americans came to realize that, for a fanatical, resourceful, and patient enemy, there are neither ethical bounds nor societal mores to delineate the nature of the target, the weapon of choice, or the scale of the violence. To put it another way, for these enemies there are no rules of engagement and there is no honor. Since September 11, our national sense of vulnerability has steadily risen. We have been in a near-constant state of high alert because of credible threats to our Nation's nuclear installations, power plants, transportation nodes, and other critical national infrastructures.