This isn't related to the question specifically, but this brings up an interesting divide between the broad category of "Southern Whites." For example, I would imagine that in 1976, Carter won a majority of "Southern Whites who had historically voted Democratic," considering Ford won a ton of suburban areas and did best in the most transplant-heavy states, such as Virginia, Florida and Texas. (A huge exception here is Mississippi, which makes sense, as the most conservative former Democrats who were decidedly less populist were the first ones to jump ship.)
The tendency to credit Northern migrants with being the source of new Republican votes in the South is overestimated.
Urban and suburban Southern whites who were middle- or upper-class started voting Republican for president in the 1950s and 1960s, even if their family had been living in the South for 200 years.
In Texas, from the Mexican era up until the late 20th century, most people who moved there were from the South (especially Tennessee, Kentucky, Louisiana and Mississippi). Dallas-Fort Worth was the first area to start attracting Northerners in sizable numbers in the 1950s to work for companies like Texas Instruments. Houston was a common destination for people from the Rust Belt in the 1980s.
