McCarthyism, named for Senator Joseph McCarthy of Wisconsin, was a period of intense anti-communism in the United States primarily from 1950 to 1954, when the U.S. government was actively engaged in suppression of the American Communist Party, its leadership, and others suspected of being Communists or Communist sympathizers. During this period people from all walks of life became the subject of aggressive witch-hunts, often based on inconclusive or questionable evidence. It grew out of the Second Red Scare that began in the late 1940s.
Of course the fact that Mc Carthy was for the most part correct is the real falacy here. I suppose there was no communist trying to take over the US. Joe made it all up. If you repeat a lie often and long enough people believe you.