Harris has not come out of this debate thinking that she's going to win. She continues to run as the underdog.
In the 2016 debate Trump made personal attacks on Hillary. For mostly BS reasons, but also a few legitimate reasons a lot of people had strong negative feelings about Hillary. So Trump's nasty attacks on her didn't bother people as much.
Trump's nasty attacks this time were on ... America. Nothing he says makes sense unless you watch Fox all day. 2/