From about 1955 to 1995, the dominant opinion in the United States held that the American Communist Party (CPUSA), founded in 1919 in the wake of the Communist revolution in Russia, was a small collection of admirers of the Soviet Union that never amounted to much. In the 1930s (so the story went) they mobilized a number of "popular fronts" to oppose fascism and promote various leftist causes. In the 1940s, a few Communists—probably Julius Rosenberg and (arguably) Alger Hiss—went so far as to commit acts of espionage on behalf of the Soviet Union. But Rosenberg was executed, and Hiss went to prison; so why all the fuss about domestic Communism?
Far worse than such rare cases of misplaced loyalty (in this view) was the damage wrought by opportunistic politicians who seized on the existence and supposed misdeeds of the CPUSA to alarm American public opinion and ruin the reputations of innocent liberals. One of the earliest such persecutors was Congressman Martin Dies, a Texas Democrat who in 1937 persuaded the House of Representatives to create a Special Committee on Un-American Activities, which became a standing committee in 1945 and lasted for 30 years, hounding Hollywood actors and many other victims.
But by far the greatest villain among Red-hunting politicians was, of course, Wisconsin's Republican senator Joseph McCarthy, who raised the issue of Communists in government in February 1950 and rode it triumphantly for four-and-a-half-years, acquiring an immense popular following, until the Senate itself voted to "censure" him in December 1954. He died, of liver failure induced by alcoholism, in May 1957, at the age of 48. By the 1960s the CPUSA, reduced to a few thousand members, had been almost wholly superseded by the New Left, and barely survived to see the collapse of the Soviet Union in 1991.