John Brennan supported Gus Hall's presidential candidacy in the 1970s. It drew minimal public attention when the news (CNN et al) reported that on his most recent security clearance polygraph, he disclosed that he had been a member of an organization whose goal was the overthrow of the US Government (standard question on security clearance questionnaires … though most marxists I know tend not to answer this question honestly, even on polygraphs, which are not foolproof.)
Hall was the head of CPUSA in the 1970s. What most people don't understand (though I'm sure Brennan is well aware) is that Hall was working directly for Moscow as a lobbyist (which is essentially what the CPUSA directorship has been since 1919 until the USSR went bankrupt in the 1980s).
At the time, the details about Gus Hall's activities were classified, but were declassified in recent years (congressional testimonies are now open-source, etc.)
Also, when the Mitrokhin Archives were published decades ago, the records of the money Gus Hall had been laundering from the USSR were disclosed, as well as records of his communications (and frustrations) with the COMINTERN leadership.
This article sort of touches on it: https://spectator.org/john-…
So… you wanna talk about Russian meddling and collusion in US politics? It's been going on for a century.
And as far as I know, John Brennan, and his fellow travelers at the highest echelons of the US Govt, have yet to outgrow (or denounce) the extremist pro-Bolshevik (aka "Soviet SOCIALIST") ideology of their blissfully ignorant youth. Welcome to the club!