Great comment. The subject goes way beyond "this party racist" because it's really the economic interests and arrangements that the parties cater(ed) to, for which racism, and this notion of race itself, developed out of. The way both sides dealt with the Populist movement is very important as well. Booker T Washington's "Atlanta Compromise" speech at the Cotton Expo basically sets the stage for things like "race relations" going forward, and the general approach to "lead the negro to his rightful place in life." Jim Crow order was imposed as well, which most people only view as a racial order and not an economic one.

This goes past the 50s-60s too, the time that most people associate as the Democrats becoming a party of civil rights with their base of northern liberals. At this same time you had the notion of the neighborhood, urban planning switching to these subdivisions, entire areas of housing built to accommodate people of the same economic status. This is more how northern segregation functioned, with the help of mortgage and real estate laws. Well educated northern liberals certainly didn't want low income housing projects in* their* neighborhoods, and would not elect a representative to city council who wouldn't defend their property values.