McCarthy started an investigation of the?

McCarthy started an investigation of alleged communist infiltration in the U.S. government during the early 1950s, which became known as the Red Scare. He claimed to have a list of communists working in various government positions, leading to widespread fear and paranoia. His tactics included aggressive questioning and public hearings, which often resulted in ruined careers and lives. This period eventually led to McCarthyism, characterized by anti-communist sentiment and a disregard for civil liberties.