Sixty years ago political divisions in the United States ran even deeper than today's name-calling showdowns between the left and right. Back then, to call someone a communist was to threaten that person's career, family, freedom, and, sometimes, life itself. Hysteria about the "red menace" mushroomed as the Soviet Union tightened its grip on Eastern Europe, Mao Zedong rose to power in China, and the atomic arms race accelerated. Spy scandals fanned...