The FBI chief is and has always been highly political. J Edgar Hoover was a extreme anti-communist and was investigating suspected communists, infiltrating CPUS

The FBI chief is and has always been highly political. J Edgar Hoover was a extreme anti-communist and was investigating suspected communists, infiltrating CPUSA and creating blacklists at the exact same time that McCarthy was conducting his hearings. In fact the McCarthyism acticle on Wikipedia has a whole section about the FBI. The FBI was deeply involved in McCarthyism.