My 2 cents.
Potus had to go in swinging to push Joe off balance. Trump's frequent interruptions were strategic, think from Joe's perspective - Joe's trying to talk with his team talking in one ear and Trump talking in the other. It wore him down quickly and put him on the defensive, took him off his SCRIPT.
Potus knew Wallace was comped and helping Joe. Wallace's voice was shaking as he tried to appear diplomatic but failed miserably.
I can not think of any way, under the circumstances, that Potus could have done it better. He did a brilliant job and he was fighting for us. Thank you Potus.