We’ve been seeing a see-saw effect for awhile, where without incumbency, the party last holding the Presidency loses. This reflects a general, vague dissatisfaction with the status quo, mostly felt at the emotional level instead of intellectually reasoned. The world is too complicated for the average person to really figure out, and they don’t like that. While you can distract yourself from this in innumerable ways, or paper over it with something like religion, it’ll surface when it comes time to consider new leadership.
Then, in addition to the various issues people will discuss, I think being a woman hurt Harris somewhat with latinos, where the culture prizes a more Trumpian machismo.
I somewhat agree, though I’ll point out people were doing quite well at the end of Clinton and Obama’s presidencies. They flipped to the other party anyway.