When the anthrax mailers penned the message, "YOU CAN NOT STOP US. WE HAVE THIS ANTHRAX," the threat included a chilling nuance that remains largely unrecognized. "ARE YOU AFRAID?" asked the attackers. "Yes," should have been the answer, according to some biodefense experts, who think that the anthrax spores mailed to Senators Thomas Daschle (D-- SD) and Patrick Leahy (D--VT) in the fall of 2001 represented the state of the art in bioweapons refinement, revealing telltale clues about the source. This view is controversial, however, because others dispute the sophistication of the Senate powder, and a schism now exists among...