Was a member of the Communist Party from the mid-1930s. This fact, and his collaboration on the script for the pro-Russian--who were our allies at the time--film
Song of Russia (1944) led to his being subpoenaed by the House Un-American Activities Committee in 1947. He was blacklisted for four years as an "unfriendly witness" before recanting in 1951 and "'naming names"--a decision he regretted in later years, but which allowed him to work again as a screenwriter in Hollywood.