Complex sentence: Ernst was a strong supporter of J. Edgar Hoover and the FBI, and in 1940, as head of the ACLU, he agreed to bar communists from employment there and even discouraged their membership.
Split into simpler sentences: Ernst was a strong supporter of J. Edgar Hoover and the FBI. In 1940, as head of the ACLU, he agreed to bar communists from employment there and even discouraged their membership.