Why did Mission to Moscow later become embarrassing for Warner Brothers?

Mission to Moscow (1943) became one of Warner Brothers’ biggest embarrassments because of its blatantly pro-Soviet message. While this stance was considered politically correct at the time of its release—having been produced at the request of U.S. President Franklin D. Roosevelt to encourage support for aid to the Soviet Union during World War II—it became anathema during the subsequent McCarthy era.

The film's content eventually led to studio head Jack Warner and screenwriter Howard Koch being called to testify before the House Un-American Activities Committee in 1947, as the political climate in the United States shifted toward intense anticommunism and the Cold War.1