Nick,

Biden has a more difficult task in the debate than Trump because he is playing catch-up. He has to show that he is up to the job for the next four years. He doesn't have a script like in the State of the Union address.

He can swing middle voters if Trump shows normality, moderation, and empathy (humility may be out of his reach). Trump has discussed foreign student graduates receiving green cards, which will work for him.

If Trump has the discipline to contain himself, he will win the debate and election. It's his to lose.

Biden can only win by default.