How can we avert catastrophe and hold down the number of lesser mass murders? Our best hope is to prevent al-Qaida from getting nuclear, biological, or chemical weapons and smuglling them into this country. But we need be unlucky only once to fail in that. Ultimately we can hold down our casualities only by finding and locking up (or killing) as many as possible of the hundreds or thousands of possible al-Qaida terrorists whose strategy is to infiltrate our society and avoid attention until they strike.

The urgency of penetrating secret terrorist cells makes it imperative for Congress—and the nation—to undertake a candid, searching, and systematic reassessment of the civil liberties rules that restrict the government’s core investigative and detention powers. Robust national debate and deliberate congressional action should replace what has so far been largely ad hoc presidential improvisation. While the USA-PATRIOT Act—no model of careful deliberation—changed many rules for the better (and some for the worse), it did not touch some others that should be changed.