I think you’re putting too much faith in the debates jgw..
As far as the debates go I think they may make a difference. We will see about that in close to 2 weeks. I really want to see if they actually have control over the microphones (which would be a miracle).
Unlike previous debates, I think this one may have an impact. The doubts that people have about each of the candidates will be highlighted there. Trump, as you noted, is become more strident in his fascist sentiments and retribution narrative. That, I think, is turning off independents and the rump "reasonable Republicans". His convictions are also having an impact.
Trump’s conviction may be hurting him — but it’s early (538/abc)
"Four pollsters have already conducted national polls of the 2024 presidential election entirely since Trump was found guilty, and a handful more have asked about the verdict but not the election explicitly. They show that Americans are taking the verdict seriously, and it may be giving President Joe Biden a small boost in support. However, it’s still too early to draw any definitive conclusions." I think, like Trump's corrosive effect on the social scene, this is going to drain enthusiasm from support.
I also think the narrative of Biden's age is still present - he does walk old, and his articulation has never been sharp, but is affected no question - but his mind is sharp and his wit is present. Of course, the most important aspects are, his heart is in the right place, his policies are effective, and he is the opposite of a fascist. (Even though his surviving son is the subject of a political prosecution, he is putting his faith in an impartial jury instead of bombast, abuse of the system, and denigrating all of the participants.) That, I think, will come out in the debate. I just hope he doesn't stumble on the way to the lectern.