Trump may have a tougher time debating than his supporters think he does.
Remember, he was an unknown quantity as a politician in the 2016 debates. He got a pass from some because he had no political track record to point to. He could make grandiose promises and draw on his personality (an ugly, vicious personality, but some people like that) without having to prove he could back up his claims. That's no longer true in 2020 -- Biden can easily point out that Trump was an abject failure even before the pandemic. Trump will lie, of course, but Biden can keep hammering Trump on those lies and failures.
Also, I can't help but think that Trump's bullying tactics just won't work on Biden, especially not in a year like this. Remember how Trump was stalking Clinton around the stage (in part due to his misogyny, but that's another thread)? Yeah, not only will Biden be unlikely to tolerate that, it's doubtful that can happen due to social distancing requirements. If Trump barks, Biden will likely bark back.
Biden will have to be careful, to be clear, with well-rehearsed talking points and prepared responses for as many situations as possible. But he really just has to show up proving that he won't back down and that he has a better plan than Trump... and a better plan isn't hard.