In retrospect, which were realigning elections?

[DabbingSanta]

1796: First contested presidential election.

1860: Split the nation into north vs south.  Northern areas would remain largely Republican for over 70 years.  The South would stay Democrat for a century, excluding the brief period of Reconstruction.  This really solidified the GOP as the dominant party going forward.

1932: Roosevelt's New Deal coalition and the collapse of Republican support in the Midwest following the start of the Great Depression. Democrats would retain the presidency for 20 years.

1948: Period of dealignment. This is when southern Democrats distanced themselves from the national party and voted for their best interests... at the time that was to preserve segregation and "state's rights".  Republicans began to make inroads in traditionally Democratic regions and the "Southern Strategy" unfolded.

1992: Bill Clinton really changed the map. He flipped several traditionally Republican regions which remain Democrat to this day — the west coast, Northeast, and New England,  and also temporarily repaired the New Deal coalition and kept the upper Midwest in the Democrat's column for 24 years.

2016: Suburban realignment from Republican to Democrat. Rural regions increasingly strong for the Republican candidate. Urban regions increasingly Democratic.  The divides which were developing since the period of dealignment solidified during this election, and they're unlikely to break any time soon.  Upper Midwest became competitive, and white working class voters fled the Democratic party in droves for a rebranded, populist GOP.