The CPUSA was an organization with definite ties to the USSR and that might be why membership in it was treated as special. It was part of the Communist Intern

The CPUSA was an organization with definite ties to the USSR and that might be why membership in it was treated as special. It was part of the Communist International (Comintern) that was headquartered in Russia. Its cells in some circumstances did actual spy operations on instructions from Moscow. So membership was a little bit closer to being a foreign agent than merely holding a viewpoint would make you. That article doesn't leave me with any idea what CPUSA membership actually was though. I know from another Oppenheimer bio that the organization had actual membership cards (thus "card carrying member"), but it sounds possible to be a member without a card. If yes, were you still on a membership list somewhere, like at the Comintern? Did you have to promise allegiance to the party, etc.? Idk.