Our Nation learned a painful lesson on September 11. American soil is not immune to evil or cold-blooded enemies capable of unprecedented acts of mass murder and terror. The worst of these enemies - and target number one in our war on terrorism - is the terrorist network Al Qaeda. Yet the threat to America is not limited to Al Qaeda - or to suicide hijackings of commercial aircraft. As we learned on October 4, 2001, a Florida man named Robert Stevens became the first known victim of an unprecedented act of biological terrorism.