Picking up on a state-by-state analysis I began at Swing State Project before the 2012 elections, I will try my hand here, with results including 2012 and 2016. I will use Charlie Cook’s Partisan Voting Index (PVI) when comparing counties. I know PVI itself is not the best way to gauge the partisan leanings of states, counties, or districts, but it can still be useful in making comparisons.
As we all know, most of Alabama’s counties were much more Democratic than the national average in the “Solid South” years. Central Alabama around Birmingham was less Democratic than most of the state in these years because of some Appalachian and anti-secession attitudes, from “the Republic of” Winston County to Chilton County. The Republican trend spread to Jefferson County (Birmingham) itself as well as outside of Central Alabama to Dallas County (Selma), Montgomery (Montgomery), the Gulf counties Mobile (Mobile) and Baldwin, and a little in Houston County (Dothan) in the late 1950s, due to the option of “unpledged electors” on the ballot.
The option “unpledged” appeared on the ballot again in 1960, and the Republican trend continued in the aforementioned counties, turning Dallas, Montgomery, and Jefferson more Republican as per PVI. In the counties that were already trending Republican, the bottom fell out of Democratic numbers in 1964 as most of the counties flipped to R+ PVIs. The presence of the Tennessee Valley Authority in North Alabama kept most counties in that region in the D+ PVI range. The only blue county outside North Alabama in the 1964 map is heavily black and college county Macon (Tuskegee). Also-heavily black Bullock and Greene Counties joined Macon in 1968. Washington County, along with Mobile to the south, also trended slightly Democratic.
During the Nixon years, the racial divisions in Alabama began to become more apparent, with much of Central Alabama becoming very Republican, and North Alabama and the Florida counties beginning to trend that way. Carter temporarily stopped the bleeding, but the Reagan revolution would put an end to that for the foreseeable future. The Reagan revolution brought a rapid Republican trend in most counties in Alabama, resulting in many R+ counties in 1988 as the national margin went slightly less for Bush than for Reagan.
In spite of two Southerners on the Democratic ticket in the 1990s, the Republican trend in Alabama continued, and the realignment of the counties, stalled in the Carter and early Bill Clinton years, picked up. North Alabama was the last holdout outside the Black Belt through 2000 probably because of the connections some voters there felt to the Tennessee Valley Authority and to Al Gore, who came from demographically similar Middle Tennessee.
The 2004 and 2008 elections saw the realignment pretty much consolidate, with the only Democratic counties for both elections in the Black Belt. Polarization continued into 2012 and 2016, with North Alabama catching up to most of the rest of the state, as memories of the Tennessee Valley Authority diminish with each passing day. Increasingly Democratic numbers from Birmingham made Jefferson the only county outside the Black Belt with a D+ PVI in 2016.
Here are the PVIs.
Here are the maps in slide format.