Trump has already attacked Biden, trying to imply he's too 'sick' and 'weak' to effectively govern. So, the lies about Hillary's health during the 2016 campaign don't just have to do with misogyny.
As far as whether a woman can win against Trump...haven't you been paying attention? Trump is TERRIFIED of strong women he can't grope or insult. What can he say about Elizabeth Warrnen? He's already attacked the "Pocahontas" thing, and no matter what the silly Stein voter says, people have let that go. And if Native Americans would rather vote for Trump than Warren, if they truly feel Trump is better for THEM, then power to them. Do you really see that happening, though? And outside of Trump's base, no one else really cares. Trump's base is gonna be Trump's base, no matter who he shoots in the middle of 5th Avenue. Period, full stop.
And Kamala Harris. What will he attack her with? You notice he's already stayed pretty much away from her. The only problematic thing about her is some of her policies as a prosecutor. But, again, IF she wins the nomination, do you REALLY think people, outside of Trump's loyal base again, will say "Oh, she was too hard, so I'll vote for the dude who's already proved himself a madman". (okay, so I'm simplifying, but at it's core, am I really?) They're trying the "she's not really a black woman", but I'm not sure how effective that will be. She's a woman of color, and the fact her ancestors came from India and Jamaica, rather than directly from Africa, isn't that huge of a distinction when it comes to race in America, outside of a right-wing bubble. And even they don't really care. Anything darker than pasty white is all the same to them.
I think a strong female candidate will send Trump reeling. His base already has all of the misogynists and if the (mostly Russian backed) Bernie bros, like dude posting on this thread, want to contribute to that, we'll just be louder.
My God. Don't give up already. Trump is an evil dude, but he's still just a weak-minded man, and like most misogynists, he's scared to death of strong, smart, confident women. I think a woman CAN win.