John,
There are many layered reasons why Trump won. But let's take just one.
To Democrats, it was never appreciated that Donald Trump was likable. Intelligent Americans never got this through their thick heads.
Trump was endearing when he gave helicopter rides to kids in flyover country, donned a McDonald's apron and over-fried chips, and turned a town hall into a disco. Few may have thought the gestures genuine, but it didn't matter.
Although one can become a governor or senator without likability, as in the cases of Ron DeSantis and Elizabeth Warren, it's an enormous handicap when running for president (as they discovered -- or still not).
Biden was never likable. He got the presidency on the third try after forty years with the help of COVID. Harris was never likable, although, to her credit, she improved.
Joe Biden was rammed down voter's throats twice and, thanks to him, had little choice but to choose Kamala Harris as a last-minute replacement. The outcome was not her fault.
Many thanks. Best.