Trump is the kind of guy that ignores you when you try. He did it to McCain. He did it to reporters--repeatedly.
On the other hand, Biden regularly insults people with profanity when he gets a question he doesn't like.
https://www.cnbc.com/2019/12/05/bid...mn-liar-and-fat-after-ukraine-accusation.html
https://www.foxnews.com/politics/biden-new-hampshire-lying-dog-faced-pony-soldier
https://thefederalist.com/2019/12/10/how-joe-biden-gets-away-with-calling-a-voter-a-fat-dumb-liar/
Do you really think if Trump told Blacks "If you don't vote for me, you're not really Black..." like Biden did the MSM wouldn't had his head on a plate for it. They largely gave Biden a pass.
Biden is not used to having to take serious criticism. He is unprepared to take and answer difficult and oppositional questions or comments of any sort. That's nearly all Trump gets every press conference.
On a stage alone with Trump, Biden's got a big problem facing him and a friendly moderator won't save him. I doubt that if there were a 'Candi Crowley moment' where the supposedly neutral moderator injects themselves into the debate like she did with Romney, Trump will bit their head off, not let it go. But he's not going to do it with incoherent profane babble like we've seen Biden do time and again.