Many of Oppenheimer's closest associates were active in the Communist Party in the 1930s or 1940s, including his brother Frank, Frank's wife Jackie, Kitty, Jean Tatlock, his landlady Mary Ellen Washburn, and several of his graduate students at Berkeley. Whether Oppenheimer was a party member has been debated. Cassidy states that he never openly joined the Communist Party USA (CPUSA), but Haynes, Klehr, and Vassiliev state that he "was, in fact, a concealed member of the CPUSA in the late 1930s". From 1937 to 1942, Oppenheimer was a member at Berkeley of what he called a "discussion group", which fellow members Haakon Chevalier and Gordon Griffiths later said was a "closed" (secret) unit of the Communist Party for Berkeley faculty.