The Smith Act trials decimated the leadership ranks of the CPUSA . Immediately after the 1949 trial , the CPUSAalarmed at the undercover informants that had testified for the prosecutioninitiated efforts to identify and exclude informers from its membership . The FBI encouraged these suspicions by planting fabricated evidence which suggested that many innocent Party members were FBI informants . Dennis attempted to provide leadership from inside the Atlanta penitentiary , but prison officials censored his mail and successfully isolated him from the outside world . Prison officials from the Lewisburg prison prevented Williamson from writing to anyone other than immediate family members . Lacking leadership , the CPUSA suffered from internal dissension and disorder , and by 1953 the CPUSA 's leadership structure was inoperative . In 1956 , Nikita Khrushchev revealed the reality of Stalin 's purges , causing many remaining CPUSA members to quit in disillusionment . By the late 1950s , the CPUSA 's membership had dwindled to 5,000 , of whom over 1,000 may have been FBI informants
Stalin 's purges
Great Purge
Smith Act trials of Communist Party leaders