A little history here:
The Democratic Party is generally regarded to have originated with Andrew Jackson, a slaveholder and genocidal indian fighter.
In its early years, the Democratic Party was led by southern slaveholders and the northern merchants who relied on them.
The Confederacy was led by Democratic politicos, who couldn't stomach Lincoln's election.
After the Civil War, scores of black Republican officeholders were elected.
Reconstruction was reversed, and Jim Crow created, by the Democratic State parties in the southern States.
Northern Democrats had little use for black voters. The progressive Woodrow Wilson was a racist.
Southern Democrats successfully defeated every piece of Federal civil rights legislation, including anti-lynching laws, up until 1964.
The Civil Rights Act of 1964 would not have passed without the votes of Congressional Republicans. A higher percentage of Republicans voted for it than Democrats.
And murdered by the DUMs.