The Russians wasted decades infiltrating the left attempting to gain purchase in American political life. There was the Communist Party USA, of course. Established in 1919, the CPUSA grew through the 1930s and boasted a membership of about 100,000 at the beginning of World War II. A hundred thousand! Whoop-de-doo!
Then there were the spinoff lefty parties like the Socialist Workers Party, the Progressive Labor Party, the Workers World Party, the Socialist Labor Party, the Progressive Labor Party — we could go on listing one splinter group after another with “socialist” or “labor” or “workers” in its title. They were tiny groups with memberships that were sometimes less than 100, and they would all deny being infiltrated by the Russkies, naturally. So would the “New Left” groups that came later, like SDS and The Weathermen. Nobody wanted to admit they were under Russian influence. Everything they were doing, from opposing the war in Vietnam to civil rights to fighting for free speech, was being done for completely pure reasons.
The Democratic Party would deny being under Russian influence as well, of course. But every American political party on the left was jointly infiltrated by Russian agents and the FBI or other American intelligence operations. There was a joke back in the ’70s that without membership by Russian infiltrators and FBI agents, the Socialist Workers Party would have gone out of existence. I covered a meeting of the SWP in a loft on lower Broadway in the early ’70s for the Village Voice. It looked to me like everyone there suspected everyone else of being either a COINTELPRO agent for the FBI or a KGB agent. You could have cut the paranoia with a butter knife.