In retrospect, which were realigning elections?

[pbrower2a]

1992, in the sense of the election showing that a realignment had been made. Overlay 1976 with 1992, and you will see that Clinton won a raft of states that Carter had lost in 1976, states that Democrats win in all subsequent winning elections (WA, OR, CA, NV, NM, IA, IL, MI, NJ, CT, VT, NH, ME). Note also that Carter is the last Democratic nominee for President to win TX. MS, AL, and SC unless something strange happens this year. Donald Trump is strange enough to make that happen.   

Realignments happen under the cover of landslides as the coalitions that allowed landslide elections rift. 1992 shows evidence that the old "Rockefeller Republicans" had begun to break from the GOP. Maybe they just could not get along with the constituencies that the Southern Strategy brought in. 

[pbrower2a]

2000 -- the equivalent of 48 electoral votes in states that usually went D in close elections went R and never turned back.

1992 -- a raft of states (including California, Illinois, Maine, New Jersey, and Vermont, which generally went R, have gone D and have never since come back.

1980 -- Carter had won Alabama, Mississippi, South Carolina, and Texas for the last time for a long time.

The realignment from 1976 to 2000 took three steps.

1952 -- several western states that had voted reliably for the New Deal Coalition went for Ike and have since not gone D more than once. Oddly the 1952 election looks much like the 1928 election for Hoover.   

[pbrower2a]

1800
1824
1848
1872
1896
1920
1944
1968
1992
2016

2016 is not a realignment election. 1976 to 2008 suggests a huge realignment in stages, and 2020 looks more like 2012 than anything else. Trump did not win an overwhelming win of the Electoral College and in fact lost the popular vote. If 2016 were a genuine realignment, then Trump would have won decisively in 2020.

2020 is of  course not a realigning election.

[pbrower2a]

All elections are realigning elections.

Uhhh... no. Except for 1980 and 1992, in which the President elected in the previous election lost by a large margin, the electoral maps are fairly similar between years. If five or fewer states move one way or the other, there is no real realignment. Even in 2020 the difference from 2016 was five states, and the most likely three of the states that did move from Trump to Biden would have been enough. 2020 looks like about as status-quo an election, one that the personality and performance of Donald Trump decided for the Presidency more than anyone else, as there ever has been. Voters casting off an corrupt, erratic, or incompetent incumbent is no realignment. Open-seat elections are more likely to have change.

"1980" reflects a change in American cultural life, with the rise of the Religious Right whose economics are best described for the proletariat as "Suffer in This World on behalf of the owners and managers so that you may receive your rewards in the Next" (opinion: anyone who pushes that deserves to end up in the part of Hell that most resembles an ante-bellum plantation in the old American South... as a slave), and "1992" reflects the separation of the Eisenhower/Rockefeller Republicans from the reactionary, racist Southern agrarians with whom they had little in common.

Will 2024 be a realigning election?  Looking at prior elections in which the President or his VP successor ran for another term...

elections of 1956, 1984 (only five states 'moved'), 1996, 2004, and 2012 suggest more of the same.
 
1976, in which Ford would have been a continuation of Nixon years without Nixon's "dark side" is likely irrelevant.

1992 is imaginable if one sees Joe Biden as a tiresome third term of Barack Obama for all practical purposes. We shall see.

1980 suggests a Presidential failure, but really... the political culture changed as the New Deal coalition fell apart and the Religious Right won over the Mountain South.

1964 and 1972 represent the losing Presidential candidate winning the nomination by winning the more radical wing of the Party, only for the incumbent's Party to cast that candidate as a dangerous extremist out of touch with mainstream America. Paradoxically the losing Party of that year nominated a moderate in the next election... and won. The problem with that analogy is that there is no large 'moderate' wing in the GOP.

Open seat? Anything goes.