 The Federal Bureau of Investigation (FBI) opened a file on Oppenheimer in March 1941. It recorded that he attended a meeting in December 1940 at Chevalier's home that was also attended by the Communist Party's California state secretary William Schneiderman, and its treasurer Isaac Folkoff. The FBI noted that Oppenheimer was on the Executive Committee of the American Civil Liberties Union, which it considered a Communist front organization. Shortly thereafter, the FBI added Oppenheimer to its Custodial Detention Index, for arrest in case of national emergency. Debates over Oppenheimer's Party membership or lack thereof have turned on very fine points; almost all historians agree he had strong left-wing sympathies during this time and interacted with Party members, though there is considerable dispute over whether he was officially a member of the Party. At his 1954 security clearance hearings, he 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.
