I think the UK and France have both recently shown that despite how things appear on the Internet, most people don't want a divisive populist government. Biden was not electable but I bet a lot of people will hold their nose and vote Harris so as not to run the risk of Trump/Vance.
Trump made the wrong pick to go up against Harris - I think he must have believed his own hype that the Democrats wouldn't pick her.
It's hard to know what she's actually like from media coverage but I'm hoping in the debates she will come across better than expected.