from the attached Wiki page...
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President Lyndon B. Johnson, although a southern Democrat himself, signed the Civil Rights Act of 1964 and Voting Rights Act of 1965. The evening after signing the Civil Rights Act, Johnson told aide Bill Moyers, "I think we may have lost the south for your lifetime – and mine", anticipating a coming backlash from Southern Whites against Johnson's Democratic Party.[3] As Johnson anticipated, this led to heavy opposition from Southern Democrats. However, the Democratic Party had a supermajority in the Senate with 46 of their members joining the Republican Party by voting for, while 21, all conservative, southern Democrats voted against.[4][5] Subsequent to the passage of civil rights legislation, many White southerners switched to the Republican Party at the national level. Many scholars have said that Southern Whites shifted to the Republican Party due to racial backlash and social conservatism.[6][7][8] Many continued to vote for Democrats at the state and local levels, especially before the Republican Revolution of 1994.[9]
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Not all Democratic Senators voted against the Civil Rights and Voting Rights Acts...just the racist ones...who later officially joined the Republican Party when it redefined itself as a safe haven for racists. The names and party shifts are in the public record.
Never trust someone that hides who they really are...
Link: https://en.wikipedia.org/wiki/Southern_Democrats