Why were Shelby and Rankin counties so Republican before the rest of AL & MS?

[smoltchanov]

The first GOP areas in the south were the suburbs. It took a while for rural voters to switch.

Well, almost. In some cases the first were big cities itself. Though difficult to imagine now - Atlanta, Dallas, Houston, Birmingham, Charlotte, Richmond, Memphis, even Jackson, and so on were centers of nascent "Southern Republicanism" in the same time (since 1950th in many cases) when rural areas of these states were still "pristine Democratic"

[smoltchanov]

The first GOP areas in the south were the suburbs. It took a while for rural voters to switch.

Well, almost. In some cases the first were big cities itself. Though difficult to imagine now - Atalanta, Dallas, Houston, Birmingham, Charlotte, Richmond, Memphis, even Jackson, and so on were centers of nascent "Southern Republicanism" in the same time (since 1950th in many cases) when rural areas of these states were still "pristine Democratic"

Same basic voter type though, they just had not yet moved to the suburbs.

That's true.

[smoltchanov]

Down-ballet Democrats in the South were Manchin types, so the only difference between the parties down-ballet was economic issues.

Manchin is much more liberal, then many southern Democrats were 40-50 years ago. He would be a sort of "business progressive" by that days standards... Even on economy there was plenty of conservatives among southern Democrats....