Having any female (or anyone not a white Christian male really) run after Obama was never going to go well.
Way too much change for a sadly large part of the country.
Not really. In 2016, slightly more women voted for her than they did for Obama, but black people voted for her much less than then did for Obama. What swung 2016 was Trump playing strong to his base and Clinton not playing strong to hers.
Why Biden is doing so well currently isn't because he's a perfect candidate - instead, it's that Trump has enthused the anti-Trump "base" so hard that Biden could be anyone and he'd get their vote, and Trump has saw his own base erode enough to suggest almost a landslide loss. Everyone who voted for Trump to "see what he could do" have now seen what he does and went back the other way.
If a female had run this time, she'd be in the same place against Trump as Biden is now - or to be honest, she'd be better off. Clinton lost because she was Clinton, not because she was a woman.
