re: How can Biden debate Trump?

I don't think people should get their hopes up. I think Trump is more coherent and competent than Biden by a good bit, but that was the case in 2020 and he failed to score anything resembling a definitive win.

Biden is worse now, Trump probably at least a little worse now.

Biden has been a professional politician for most of his life, if his faculties are decent that day he'll handle the situation fine (unfortunately). The risk is him losing his train of thought a bunch of times or just staring off into space while someone is asking him a question, which is a possibility. Moreover, people have already baked in the concept of Biden as your mostly friendly semi-senile grandfather, so him coming off like that isn't going to move the needle.

For it to meaningfully matter I think "moderates" need to walk away going "ok having this guy as President is just too embarrassing" (which can also be negated by Trump's antics).