The Democratic establishment thought Biden was their only shot at beating Trump, so they engineered it so that he got the nomination, knowing full well (I believe) that he wasn't all there. It's really a shame that this is what politics is in this country, but there you go.
God forbid a fully lucid candidate like Bernie get a shot. No, they had to smear him because he was doing too well, in favor of a candidate that should never have really been seriously considered.
I'm glad Trump is out. I'd rather have someone incompetent in office than someone who's both incompetent and has no respect for decorum, democracy, or the rule of law. But my God does Biden suck.
Whether you're on the left or the right politics is just a shit show in America right now.