Rep. Samuel Dickstein for one. I don't recall reading that others were. Staffers, yes. Executive branch staffers (from low to high) yes. The OSS was riddled with Soviet agents during WW2. The Soviets were tipped to Venona vulnerability when a high level CIA/CI person (Engleton?) gave a heads up to the MI6 liaison who was actually a soviet agent (one of the "Cambridge 5"). The decrypts continued on old stored up messages, but not on new ones.