 He just has to look like he's vigorous and not an old geezer. We've seen him perform in high stakes events before, like the State of the Union. For Trump, his campaign has set the bar very, very high. They've talked about how great a debater he is. They expect him to be vigorous. They say he'll wipe the floor with Joe Biden. So the Trump team has set the bar low for their opponent and high for their candidate, which usually campaigns don't want to do.