In Mississippi, Black people prefer to vote for Black people, and White people prefer to vote for White people.
Look at any high shool or college lunchroom and you will find a similar distribution of people sitting together. I don't think this is racism. In the 1960's in my high school in Missouri, the kids seated themselves in at least five different groups: Black students, Town merchants' kids, Commuters' kids, Baptist kids and a table or two for 'assorted'.
It means that people trust people who look like themselves. You vote for people who think like yourself, don't you?
It COULD mean that there is more racism in Mississippi, but the traditional, bedsheet-wearin', cross-burnin', rebel yellin' Mississippians moved en masse to the Republican Party in the late 1960's, Trent Lott and his cohorts are the sons and grandsons of these guys. People have become less racist with every generation, but such changes take time.