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The Wikipedia website states: "Before the film was released, a fight broke out over the film's script clean-up, which happened between Director Irwin Winkler and former blacklisted writer Abraham Polonsky: through others, Polonsky learned Winkler changed the political convictions of the De Niro character. He resented the change-over. In the re-write, David Merrill was changed from a Communist Party member to a relatively apolitical Liberal. Winkler based his conception of Merrill on blacklisted Director John Berry, who would come back to Hollywood film, though it took time to get off the blacklist. Polonsky was so offended that Director Irwin Winkler changed the main character, that he not only had his name taken off of the picture, he also refused an Executive Producer credit that would have earned him a substantial fee."
Martin Scorsese portrays a fictional director called "Joe Lesser". This character is based on Director Joseph Losey, who left Hollywood in the 1950s, rather than face the HUAC examinations.
Blacklisted Writer and Director Abraham Polonsky wrote the original screenplay for the film. When Irwin Winkler decided to re-write the script by changing De Niro's character from a Communist to a more generic Liberal, Polonsky had his name removed from the film's credits. "I wanted it to be about Communists, because that's the way it really happened. They didn't need another story about a man who was falsely accused", he said in an interview in the New York Times.
David Merrill's (Robert De Niro's) climactic courtroom speech is an almost verbatim lift of a speech made by lawyer Joseph N. Welch in a McCarthy hearing in the 1950s.
Abraham Polonsky, a victim of the blacklist, was so offended that Irwin Winkler changed the main character from a Communist Party member to a Liberal, that he not only had his name taken off of the movie, he also refused an Executive Producer credit that would have earned him a substantial fee. Polonsky was very vocal in the press about his anger with Winkler, and his disapproval over the resulting movie.
According to the article "McCarthyism Made Simple" by Jonathan Rosenbaum published in "The Chicago Reader", this picture was "the first Hollywood feature devoted in its entirety to the film industry blacklist." The earlier Martin Ritt-directed film The Front (1976) dealt with television.
Martin Scorsese: As Director Joe Lesser, who was based on real-life film Director Joseph Losey, who spent the rest of his career in the UK after being blacklisted.