A number of America's foes and potential foes are actively conducting research on chemical, biological, or nuclear weapons. As motives change and their self-imposed constraints erode, today's terrorists seem more interested in running up high body counts than in advancing a political agenda. The nerve gas attack in Tokyo's subways may inspire repetition. Even the fact that we are publicly devoting so much attention to the topic may awaken terrorist interest. At the same time, we cannot conclude that catastrophic terrorist attacks involving weapons of mass destruction are imminent or inevitable.
Historical analysis provides no basis for forecasting such incidents.
There is no inexorable progression from truck bombs to weapons of mass destruction. With one possible exception, it is not clear that any organized terrorist group is planning to use chemical or biological weapons. In the more than four years since the Tokyo attack, no group has attempted to do anything like it. This fact gains significance when we note that past terrorist and criminal innovations airline hijackings, political kidnappings, malicious product tampering were promptly imitated. And terrorist attacks involving chemical or biological agents, if they do occur, are likely to remain rare events they will not become the truck bomb of the next decade.