When a study by the Centers for Disease Control concluded in the late 1980s that the link between Agent Orange and various cancers was too tenuous to prove, it looked as if the many years of highly charged debate over the notorious defoliant used in Vietnam were over. Only 1,000 of the 39,000 claims made would be paid out; the rest of the veterans would be left with nothing but bitter memories.
The controversy did not die down, however. Veterans groups continued to blame the dioxin-tainted herbicide for everything from birth defects to degenerative nerve diseases. After a federal judge ruled...