Oppenheimer himself at his 1954 security clearance hearings denied being a member of the Communist Party, but identified himself as a fellow traveler, which he defined as someone who agrees with many of the goals of Communism, but without being willing to blindly follow orders from any Communist party apparatus.
http://en.wikipedia.org/wiki/Robert_Oppenheimer
Oppenheimer destroyed himself, allying himself with the only orthodoxy [but somehow being not orthodox] that was more murderous than fascism.