1) Racism: I mean... there was a whole movement born out of Obama being elected. Racism has been, for as long as I can remember, a dog whistle the Republican party would blow in every Presidential election but with Trump, that was now more open and obvious to the point of it being basically a bullhorn.
2) Sexism: We just have to look back 8 years to see the impact of sexism in our Presidential races. While Clinton wasn't a great candidate, if the same policy/behaviors had been from a male democrat, I think things might have been different... or that politician would have been a republican.
Quick side note: It's also telling that we've only had 2 women Presidential candidates and 2 non-white Presidential candidates who have run in the general (and one of each wasn't there due to primary results).
3) Short memory span: nobody remembers how bad Trump was and certainly they don't remember how awful he was with covid... or they are in his base and think he did fine somehow.
4) "It can't possibly be that bad therefore it's not and won't be": this is the same intellectual dysfunction that people have with all sorts of things, including covid and climate change. It can't be that a white supremacist would be the nominee. It can't be that a basic mob boss is the nominee of a party for the Presidency. It can't be that he's being that openly dumb. Therefore, it's not. Also, Project 2025 is a nightmare scenario, so it can't be that they actually want to implement it.
5) Back and forth between the parties to resolve things: generally if the world is seen as being bad, it doesn't matter whose policies are actually better for the situation, one side had 4 years, give the other side a chance (even if the one side didn't actually have power during that time because they didn't have Congress). I had a colleague who felt this way prior to Trump. He and I are no longer talking so I don't know if he would still feel this way... but I can easily see this being a rational in combination with the third and fourth for many to decide that it was time to vote for a Republican.
6) It's the economy stupid.... but the economy is not an easy topic. People know that things are more expensive now than they were. Whatever the reason for that increased expense, they blame the current administration (a not uncommon scenario) and Harris was tainted by being in that administration.
7) A general shift toward caring less about others. In the spring of 2020, there was a general push to see everyone as part of the same community. Republicans generally pushed against being concerned about the public's health. As time went by, that push against taking precautions for the general public's safety became more and more accepted by the broader population. By spring 2021, the "we're in this together" messaging from Democrats and media had been switched to "protect yourself for your own sake and don't worry about others." A natural extension of this is that men shouldn't worry about women, whites don't have to worry about non-whites, straight people don't have to ... you get the picture. And even if you were a member of a targeted population, as long as you're not overly concerned or think that you won't be more targeted than otherwise, well, then it's not like this election is actually that great a concern.
8) "Vote for me because my opponent is awful" worked in 2020 because we were in the thick of Trump-Terror... but it's a poor motivational message, especially when you combine with element 4 above.
