Protagoras lived before debate was invented, so he invented it. In Greece. He did this while he was wondering whether virtue could be taught; but never figured that out. What he did figure out was that words are powerful and they function powerfully when used by people talking about two sides of an issue. He didn’t call it debate. He called it wrestling.
He saw intellects grappling through the metaphor of wrestling and wrote a book The Technique of Eristics (“On wrestling”) to teach argument to other folks.
Upcoming election debates may not have the advantage of true wrestling, in which the winner is the person who makes the most convincing argument. Not what he looks like. Not how nervous he is. Not how much we like his manners, but which argument is the stronger.
One thing the debates likely will accomplish is spawn argument about WHO won, which suggests we still have a lot to learn about debate.