Butler was dismissed from the Union Army after his failures in the First Battle of Fort Fisher, but soon won election to the United States House of Representatives from Massachusetts. As a Radical Republican he opposed President Johnson's Reconstruction agenda, and was the House's lead manager in the Johnson impeachment proceedings. As Chairman of the House Committee on Reconstruction, Butler authored the Ku Klux Klan Act of 1871 and coauthored the landmark Civil Rights Act of 1875.