It's plausible. Angry flustered off-topic lying Trump is something people have been seeing for over 8 years. He spent too much time digressing about the past even when he was trying to correct Harris when the moderators wouldn't step in (which is as it should have been for both candidates), but did manage to close with at least one key point: what was done during the prior administration?
He benefits from the perception that the moderators were actively on-side for Harris. A couple of interventions against Harris would have mitigated that, but there were none. Whatever angels-on-the-head-of-a-pin debates people want to have about the substance of "these things merited correction; nothing else did", the appearance is manifestly one-sided. Having read parts of the transcript, I'm struck by how often the moderators felt they needed to interject at length. That's not a role for moderators. If candidates are bullsh!tting each other, the candidates should also be policing each other. He tells a lie or shades the truth; she counters with a straight statement of historical facts. If the opposing candidate doesn't know the point well enough to elucidate facts, that's on the opposing candidate - the moderators aren't there to be a backup set of notes on cue cards. The perception of Democratic-favouring bias is aggravated by past performances - Crowley's incorrect fact-check, Brazile's admission of passing questions beforehand. One of Trump's themes is that the establishment is out to get him. Whether intended or not, fair or not, this debate bolstered that theme.
Conversely, Harris has gotten about as far as she can with hype, sympathetic public relations, and presenting well. Adopting facial expressions of condescending amusement - or too much repetition of any other kind of unseriousness - typically isn't well-received by people not already sympathetic. Having seen some clips, I was reminded of Biden's repeated dismissive chuckling during his debate with Ryan. I suppose it plays well with some people, but not all. I doubt Harris can run out the remaining 8 weeks without having to explain some of her policy position reversals or be specific about how she would govern differently (break continuity with the Biden administration). Some of the questions were opportunities to do so, but she's still inclined to throw out a lot of vision and fluff. Her reluctance to face adversarial Q&A formats limits her opportunities to be more informative. The closer the election date gets, the fewer opportunities there are and the harder it's going to be to tell people a little bit at a time to mitigate whatever damage results. The theme all this relates to is "these people think they're smarter than you, and don't have to explain themselves".