Do Debates Matter?

Eventually, yes:

...while debates rarely prompt immediate, measurable change, post-debate evaluations can. In 1992, right after the first debate, 24 percent of viewers said Ross Perot had won. By the very next night, amid positive reviews of Perot’s performance, that perception had grown to 37 percent among people who either had watched it, or heard or read about it. And Perot’s support did advance, from 6 percent before the debates to 17 percent after them.