Biden is unique in that he seems to know how to deal with people like Trump one-on-one. I think he likes to think of himself as someone who can stand up to a bully. Hillary certainly couldn’t.
I think this debate is unique, in that the two candidates aren’t really going to debate on policies. It is performative for both of them. What they say matters less than how convincing they are in saying it.
Biden is betting that a lot of his problem in the polls is due to concerns over his age. If he can parry Trump’s verbal shots while showing the same energy he did in the SOTU, then he may start turning those polls around. But it’s a bet, it’s not a certainty at all.
I wonder if they scheduled the debate early on purpose, so that if Biden has a poor showing his oncologist will all of a sudden diagnose him with cancer in his $ORGAN, reluctantly leading him to bow out.