McCarthy was a quiet and undistinguished senator until February 1950, when he accused that 205 Communists had infiltrated the State Department creating a disturbance and catapulted him into headlines across the country. Upon subsequently testifying before the Senate Committee on Foreign Relations, he was unable to produce the name of a single  “card-carrying Communist” in any government department. Nevertheless, he gained  increasing popular support for his campaign of accusations by using the fears and frustrations of a nation weary of the Korean War and surprised by Communist advances in eastern Europe and China. McCarthy proceeded to instigate a nationwide, militant anti-Communist “crusade”; to his supporters, he appeared as a dedicated patriot and guardian of genuine Americanism, to his detractors, as an irresponsible, self-seeking witch-hunter who was undermining the nation's traditions of civil liberties.

 McCarthy was reelected in 1952 and obtained the chairmanship of the Government Committee on Operations of the Senate and of its permanent subcommittee on investigations. For the next two years he was constantly in the spotlight, investigating various government departments and questioning innumerable witnesses about their suspected Communist affiliations. Although he failed to make a plausible case against anyone, his colourful and cleverly presented accusations drove some people out of their jobs and brought popular condemnation to others. The persecution of innocent persons on the charge of being Communists and the forced conformity that this practice engendered in American public life came to be known as McCarthyism. Meanwhile, less flamboyant government agencies actually did identify and prosecute cases of Communist infiltration.

McCarthy's increasingly irresponsible attacks came to include President Dwight D. Eisenhower and other Republican and Democratic leaders. His influence waned in 1954 as a result of the sensational, nationally televised, 36-day hearing on his charges of subversion by U.S. Army officers and civilian officials. This detailed television exposure of his brutal and truculent interrogative tactics discredited him and helped to turn the tide of
 public opinion against him.

 When the Republicans lost control of the Senate in the midterm elections that November, McCarthy was replaced as chairman of the investigating committee. Soon after, the Senate felt secure enough to formally condemn him on a vote of 67 to 22 for conduct “contrary to Senate traditions,” and McCarthy was largely ignored by his colleagues and by the media thereafter.