Why did Donald Trump win, even after inciting an insurrection, being convicted of felonies, facing two impeachments, and all his other excesses? It was combination of factors with one that stands out above all the rest.
There is a segment of voters who would've voted for a Democrat who wasn't a woman or of black and Indian descent. It might have been large enough to swing the election. Kamala Harris was also at a significant disadvantage jumping in the race three months before the election. Trump has been running for nine years, which makes it harder for others to define him. Harris, who ran as a centrist, was more easily defined as a radical leftist by Trump. Both points suggest it would've been wiser for the Democrats to stay with Biden, who actually won the primary, than to switch to Harris. Biden may not have won, but he wouldn't have done any worse.
The biggest issue is with the electorate. There are far too many low information voters. That allows Trump to get away his constantly lying. Voters don't know enough not to believe him. It enabled Trump to define Harris as a radical leftist despite all evidence to the contrary. Trump can play on people's fears about trans athletes and illegal immigrants, who don't have any impact on the lives of almost every American. Rural and suburban dwellers fear cities even though crime is way down.
Most Americans don't even know how the government or the economy works. So if the price of eggs rises, they believe the president is at fault. Yet, when policy makers work to deregulate water safety and people develop diseases and die as a result, they can't comprehend the government's impact.
Fundamentally, the electorate needs to become more knowledgeable at the very moment it's becoming much less so. This is the main issue that needs to be solved.