Professor Deborah Lipstadt examines a chilling new trend in historical revisionism: disavowing the deaths of six million Jews in Nazi concentration camps. Her new book, "Denying the Holocaust" (Free Press) traces the rise of this opposition: its practitioners' change in influence as isolated pamphleteers and cranks forty years ago to their point today, where a new poll found one fifth of the American public think it seems "possible" that the Holocaust never happened.