Biden was uninspiring but ultimately did okay on a few things. The things that screwed him were inflation - some of which was Trump's fault - and his mental state, which can happen to anyone at that age. The inflation followed Harris in her run, as people were fondly remembering 2017-2019 and the era of lower prices. They thought putting Trump back in office would reverse the trend.
Well, now he's drastically kicking prices up left and right with no end in sight. It's not even macroeconomic factors doing this like it was with COVID; it's purely the strokes of his pen.
The bottom line is the ultimate thing that matters in American politics, as it is everywhere. The talk about democracy, institutions, rights, etc. are all window dressing. "It's the economy, stupid", and it's getting noticeably worse.
Of course, I could also be totally wrong like everything else has been for the last 10 years when it comes to predicting the downfall of that tyrant.