US elections that "broke" the other side?

[Vosem]

2012 would be the big one for the modern GOP; it forced a reckoning that many socially-conservative stances that would've been winners in the recent past were unpopular, and because Romney ran what was (considered by most in the party to be) such a picture-perfect campaign, there was a scramble to look for alternatives. 2012 also fed into Democratic narratives about the reasons they had an advantage in society (since it substantially was won on the grounds of high turnout from very blue minorities and youth), so that also caused panic. (I think in the long run 2012 also kind of broke Democrats a little, actually, because they have attempted to analyze every result since 2012 as if it were 2012 again, and it's been very tough for them to admit that "high turnout among minorities and youth" is just not a sustainable winning strategy).

2016 also did, but I think less so than 2012. In 2016, the Republicans ran what was (considered by most in the Democratic Party to be) a comically bad campaign, making every mistake in the book; they still won, but in a flukish way as a result of a high third-party vote which was unrepeatable. There was then a conceit within the Republican Party that this sort of campaign would be usually successful, which was wrong and has bitten the party in the ass on some occasions. Democrats reacted nihilistically and decided that "nothing matters", and moved left on fiscal/economic issues, resulting in some blunted victories.

(The point is: after 2012, Democrats decided that "we can just do this every time", and so fell into a series of traps. After 2016, Republicans decided that "we can just do this every time", and so fell into a series of traps. The Republican version of this is mostly worse, in that 2016 wasn't even a real popular-sentiment victory, but at the same time many candidates feel like they don't have the personality to try to ape Trump '16, while every Democrat tries to ape Obama '12 and this is often not a thing that works.)