Here's what I expect:
For Harris to "win": She needs to be able to go toe to toe with Trump. Any stuttering, nervousness, or uneasiness will be preyed upon, both immediately by Trump and afterwards in soundbytes and attack ads. She cannot have a "......we finally beat medicaid!" moment. She needs to show that she can stand up to him and give it as good as she can get it in real time. She is definitely at a bigger risk here. Trump will gaffe every 30 seconds and nobody will bat an eye. One gaffe by Harris could cost her the election. Trump will be spouting his firehose of lies while Harris won't be able to fact-check 1% in real time. Harris needs to be pretty much perfect from start to finish. Any mistakes can and will be exploited.
For Trump to "win": Expectations are really low here. He's not trying to reach new voters. He opely says he doesn't care about policy. He is doubling down on the racism and misogyny of his base. All he needs to do is control the narrative. Ignore the rules, talk louder, interrupt mid-sentence. It doesn't matter what gibberish he vomits out of his mouth. None of it will cause him to lose a vote. All he needs to do is dictate the narrative and pace of the debate. He solidifies his position among his base as the mysoginist who will put women back where they belong, and gives undecided voters doubt about whether she will be able to handle the pressure. I think as long as Trump forces everybody to play his games by his rules as he usually does, it'll be a "victory" for him. Or at the very least a tie. As long as he can portray himself as the strongman going forward, he's really got nothing to lose.