It was a Republican President, Dwight Eisenhower, who signed the Civil Rights Act of 1956, sometimes called the Civil Rights Act of 1957, removing barriers to Black voting.
It was this same Republican President who sent federal troops to Little Rock, Arkansas to allow Black students admission to High School there.
The Civil Rights Act of 1964 could not have been passed without a huge majority of Republicans voting for it because many Democrats refused to support it.
Martin Luther King was a registered Republican not a Democrat.
Democrat Senator Robert Byrd was a Exalted Cyclops in the KKK. He personally filibustered the landmark Civil Rights Act of 1964.