His supporters aren't rational, trump could be older and less coherent than Biden and they wouldn't care. We can't measure them in the same ways, as their supporters don't look for the same things. People who will vote for trump don't care what trump sounds like, as long as it's trump. The people we need to show up and vote for Biden do care what he sounds like and how cogent he is.
This is the real problem we face. The problem isn't getting people not to vote for trump, because people will, we need people to show up and vote for someone else.
Republicans win when no one shows up, Democrats win when everyone shows up. We need to make sure the candidate for the Dems is worth showing up for.
As much as I want to believe, it looks like every major city is experiencing downtime. Looks like selectively used data.