Your maps, plus Ebert's, do show one important thing: how successful Nixon's "Southern Strategy" has been in the last 40 years in getting segregationist assholes to switch parties. When you set policies to attract a certain attitude, you assume that attitude.
I didnt want to debate but…
In the late 40s the Dixiecrats (as Ken pointed out) brought that to the Republican party. Then Johnson drove more racists away from the Democratic side when he pushed through civil rights. The Republicans inherited it. Nixon is often frowned on but I believe won by a greater margin than any President in history only losing MA and DC. So in the early 70s, the US was Rep by that map breakdown. The south then voted for Carter which was after Nixon.