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McCarthyism, name given to the period of time in American history that saw U.S. Sen. Joseph McCarthy of Wisconsin produce a series of investigations and hearings during the 1950s in an effort to expose supposed communist infiltration of various areas of the U.S. government. The term has since become a byname for defamation of character or reputation by means of widely publicized indiscriminate allegations, especially on the basis of unsubstantiated charges.