"Candidates are used to being on camera, but the big difference in the debates is that they're not used to being on the same stage with their opponents," said Mitchell McKinney, a communications professor at the University of Missouri and co-author of three books about presidential campaign rhetoric. "This is the only moment that they are literally within arm's reach. So they're responding to one another. They have these nonverbal tics that are a tell. They're disgusted. They don't want to be there. That has gotten some of them in trouble."
"In debates, you expect attacks, aggression, conflict," Mr. McKinney said. "But do the candidates spar with each other in a way that remains courteous, rather than snarky and belittling? That is beneath what we regard as presidential timber."