I think his physicality is really going to be a factor here. He's very big--around 6'2"--and despite his age he's very high-energy, to borrow his phrase. That's going to come across when he's compared to shriveled, sickly Hillary. When he embarrasses her we know her reaction: phony smile, chuckle, looking down at cheat sheet, head shake, rolling eyes with fake smile. While she's doing that, Trump is burying her, loudly, and gesticulating. He has the energy to do that for 2 hours. On the subconscious level the physical contrast is going to favor him in the eyes of the viewing public greatly.
Could it get tedious? Yeah, it could. But he's good at not answering questions (in that sense he's a talented, natural politician) and will continually give vague answers to policy questions and find ways to attack Hillary. And during those attacks all we'll get is the chuckling and head shaking. She's going to look weak and guilty next to Trump's confident, aggressive body language. The white knights won't like the big guy picking on the weak old grandma, but most Americans hate both of them so not many overall will sympathize with her. Especially as Trump continually rattles off scandal after scandal that she can only answer with chuckles, head-shakes, and weak responses like "what difference does it even make."
