J. Edgar Hoover was hunting Communists in 1924 when he was named Director of the Bureau of Investigation, the predecessor of the FBI.
Later in the 50's Senator Joe McCarthy was hunting Communists who had worked their way into FedGov, and the problem he ran into was that he was outnumbered. There were so many Communists embedded in FedGov and elsewhere they were able to shout him down. He died at just 48 years of age, censured and despised.
Yet when the Soviet Union "fell", KGB archives identified 221 Communists who had jobs in the Hoover Administration in 1941!!! So you can imagine how many were in place in the '50's.
Anatoliy Golitsyn defected in December 1961 and informed the CIA that US FedGov was thoroughly penetrated, there was a very highly placed mole in US Intel code named Sasha working for the Soviets, and that the US was on the wrong end of a very sophisticated, long-term deception that was an existential threat to the USA. The CIA's best counter-intelligence asset, James Jesus Angleton, perhaps one of the best ever, debriefed Golitsyn and certified his bona fides. Yet Golitsyn was correct - the Soviets even then owned the highest levels of USG. Golitsyn was deemed a fraud and Angleton was smeared to the point that his credibility was reduced to nothing.
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