<human>:  What was the name of the senator who led the investigation into communists in the USA?
<bot>: The name of the senator was Joseph McCarthy. He was the head of the Senate Permanent Subcommittee on Investigations. He conducted a number of investigations into communist influence in the US government. The most famous of these was his investigation into communists in the US Army, which he conducted in the 1950s. McCarthyism refers to the anti-communist witch hunt that took place in the United States during the Cold War.