The most visible face of terrorism--which is embedded in the conflicts in Afghanistan, Pakistan, and the border region between the two countries--could mask an even bigger danger. In the world of counterterrorism, which includes the quiet work of intelligence gathering at home, abroad, in prisons, in mosques, and in Internet chat rooms, Western analysts are working hard to understand one of the most frightening threats, that of nuclear terrorism.

In his appraisal of this menace, Todd M. Masse explores the likelihood of an attack by examining the two major schools of thought on the...