Think about this - His CIA interview occurred in 1980 and he had voted for the Communist candidate way back in 1976. Obviously the CIA has been compromised for a very long time
In 1976 without the internet anyone could walk into a public library & look up everything they needed to know about CPUSA chairthing Gus Hall, who was a slavish Stalinist well to the left of Angela Davis.
Brennan knew exactly what he was doing.