IMO These debates don't change anything in the modern era.
TLDR at the bottom.
George W. Bush allegedly won at least two of his three debates against Gore and John Kerry allegedly won two out of three debates against Bush. Both Kerry and Gore were allegedly smarter, more prepared, and better at speaking off the cuff than Bush, but that doesn't matter because Bush had more charisma and he was able to memorize all the talking points he used stumping during his campaign. The canned material worked.
The Palin vs Biden debate went about the same. Palin held her own by memorizing the talking points and only made minuscule errors despite the fact that she was practically clueless about actual international and domestic history, policy, and events. The expectations for her were so low that some people credited her with the win.
The thing about these debates is that in this divided political landscape the partisans will always cheer for their side regardless of the quality of their anointed one's ideas, intelligence, knowledge, or rhetorical skill. And if the candidates don't say something super stupid (Ford-Carter debate), the non-partisans in the middle just pick the candidate with more charisma.
TLDR: All Trump needs to do is to quote some talking points and chuckle and he'll do fine at the debate. All you need is a little prep, a little charm, and a good attitude and nothing can go wrong.