In the late 1940s, the shock waves that followed the sensational news of Communist spy rings operating deep inside the government in Washington, D. C., affected American politics, culture, and society for the next decade. The first reverberations of spy activities began in the summer of 1945 when six people, including a high-ranking State Department official, were arrested for passing classified government documents to the left-leaning journal, Amerasia, edited by Philip Jaffe, a friend of Communist Party chieftain Earl Browder. Shortly afterward, the American public learned of other spy operations through the revelations of Elizabeth Bentley, a former Communist and courier for a Soviet spy network; Igor Gouzenko, an intelligence officer working in the Soviet embassy in Canada; and Whittaker Chambers, a former underground Communist agent in the 1930s.

These reports revealed the existence of an atomic spy ring headed by Julius and Ethel Rosenberg; two spy rings operating in Washington, D. C., that implicated high officials in the Roosevelt administration, including White House aide Lauchlin Currie, Assistant Secretary of the Treasury Harry Dexter White, and Alger Hiss, a former State Department official in the Roosevelt and Truman administrations. Other cases followed.

Fears of widespread Communist infiltration into American institutions intensified as U.S. relations with the Soviet Union deteriorated, China fell to the Communists in 1949, and the Korean War began in 1950. Republicans used the spy cases to attack Roosevelt's New Deal government and its successor, the Truman administration, for having ignored the insidious nature of Soviet communism.