The left had become very influential in the hard times of the thirties, and during the war against Fascism. The actual membership of the Communist party was not large-fewer than 100,000 probably-but it was a potent force in trade unions numbering millions of members, in the arts, and among countless Americans who may have been led by the failure of the capitalist system in the thirties to look favorably on Communism and Socialism. Thus, if the Establishment, after World War II, was to make capitalism more secure in the country, and to build a consensus of support for the American Empire, it had to weaken and isolate the left.

Two weeks after presenting to the country the Truman Doctrine for Greece and Turkey, Truman issued, on March 22, 1947, Executive Order 9835, initiating a program to search out any "infiltration of disloyal persons" in the U.S. government. In their book The Fifties, Douglas Miller and Marion Nowack comment:

Though Truman would later complain of the "great wave of hysteria" sweeping the nation, his commitment to victory over communism, to completely safeguarding the United States from external and internal threats, was in large measure responsible for creating that very hysteria. Between the launching of his security program in March 1947 and December 1952, some 6.6 million persons were investigated. Not a single case of espionage was uncovered, though about 500 persons were dismissed in dubious cases of "questionable loyalty." All of this was conducted with secret evidence, secret and often paid informers, and neither judge nor jury. Despite the failure to find subversion, the broad scope of the official Red hunt gave popular credence to the notion that the government was riddled with spies. A conservative and fearful reaction coursed the country. Americans became convinced of the need for absolute security and the preservation of the established order.

World events right after the war made it easier to build up public support for the anti-Communist crusade at home. In 1948, the Communist party in Czechoslovakia ousted non-Communists from the government and established their own rule. The Soviet Union that year blockaded Berlin, which was a jointly occupied city isolated inside the Soviet sphere of East Germany, forcing the United States to airlift supplies into Berlin. In 1949, there was the Communist victory in China, and in that year also, the Soviet Union exploded its first atomic bomb. In 1950 the Korean war began. These were all portrayed to the public as signs of a world Communist conspiracy.

Not as publicized as the Communist victories, but just as disturbing to the American government, was the upsurge all over the world of colonial peoples demanding independence. Revolutionary movements were growing-in Indochina against the French; in Indonesia against the Dutch; in the Philippines, armed rebellion against the United States.

In Africa there were rumblings of discontent in the form of strikes. Basil Davidson (Let Freedom Come) tells of the longest recorded strike (160 days) in African history, of 19,000 railwaymen in French West Africa in 1947, whose message to the governor general showed the new mood of militancy: "Open your prisons, make ready your machine guns and cannon. Nevertheless, at midnight on 10 October, if our demands are not met, we declare the general strike." The year before in South Africa, 100,000 gold mine workers stopped work, demanding ten shillings (about $2.50) a day in wages, the greatest strike in the history of South Africa, and it took a military attack to get them back to work. In 1950, in Kenya, there was a general strike against starvation wages.

So it was not just Soviet expansion that was threatening to the United States government and to American business interests. In fact, China, Korea, Indochina, the Philippines, represented local Communist movements, not Russian fomentation. It was a general wave of anti- imperialist insurrection in the world, which would require gigantic American effort to defeat: national unity for militarization of the budget, for the suppression of domestic opposition to such a foreign policy. Truman and the liberals in Congress proceeded to try to create a new national unity for the postwar years-with the executive order on loyalty oaths, Justice Department prosecutions, and anti-Communist legislation.

In this atmosphere, Senator Joseph McCarthy of Wisconsin could go even further than Truman. Speaking to a Women's Republican Club in Wheeling, West Virginia, in early 1950, he held up some papers and shouted: "I have here in my hand a list of 205-a list of names that were made known to the Secretary of State as being members of the Communist Party and who nevertheless are still working and shaping policy in the State Department." The next day, speaking in Salt Lake City, McCarthy claimed he had a list of fifty-seven (the number kept changing) such Communists in the State Department. Shortly afterward, he appeared on the floor of the Senate with photostatic copies of about a hundred dossiers from State Department loyalty files. The dossiers were three years old, and most of the people were no longer with the State Department, but McCarthy read from them anyway, inventing, adding, and changing as he read. In one case, he changed the dossier's description of «liberal» to "communistically inclined," in another form "active fellow traveler" to "active Communist," and so on.

McCarthy kept on like this for the next few years. As chairman of the Permanent Investigations Sub-Committee of a Senate Committee on Government Operations, he investigated the State Department's information program, its Voice of America, and its overseas libraries, which included books by people McCarthy considered Communists. The State Department reacted in panic, issuing a stream of directives to its library centers across the world. Forty books were removed, including The Selected Works of Thomas Jefferson, edited by Philip Foner, and The Children's Hour by Lillian Hellman. Some books were burned.

McCarthy became bolder. In the spring of 1954 he began hearings to investigate supposed subversives in the military. When he began attacking generals for not being hard enough on suspected Communists, he antagonized Republicans as well as Democrats, and in December 1954, the Senate voted overwhelmingly to censure him for "conduct…unbecoming a Member of the United States Senate." The censure resolution avoided criticizing McCarthy's anti-Communist lies and exaggerations; it concentrated on minor matters on his refusal to appear before a Senate Subcommittee on Privileges and Elections, and his abuse of an army general at his hearings.

At the very time the Senate was censuring McCarthy, Congress was putting through a whole series of anti-Communist bills. Liberal Hubert Humphrey introduced an amendment to one of them to make the Communist party illegal, saying: "I do not intend to be a half patriot… Either Senators are for recognizing the Communist Party for what it is, or they will continue to trip over the niceties of legal technicalities and details."

The liberals in the government were themselves acting to exclude, persecute, fire, and even imprison Communists. It was just that McCarthy had gone too far, attacking not only Communists but liberals, endangering that broad liberal-conservative coalition which was considered essential. For instance, Lyndon Johnson, as Senate minority leader, worked not only to pass the censure resolution on McCarthy but also to keep it within the narrow bounds of "conduct… unbecoming a Member of the United States Senate" rather than questioning McCarthy's anti-Communism.

John F. Kennedy was cautious on the issue, didn't speak out against McCarthy (he was absent when the censure vote was taken and never said how he would have voted). McCarthy's insistence that Communism had won in China because of softness on Communism in the American government was close to Kennedy's own view, expressed in the House of Representatives, January 1949, when the Chinese Communists took over Peking. Kennedy said: