 They are known quantities. They both know that. And they know each other. They debated each other four years ago, twice. And they both have records as presidents that they're going to attack each other about. What about the campaign? How much weight are they putting on this debate tonight? Do they see it as just another thing that they've got to check off and then get into everything that's coming up? Or could there be a make it or break it moment tonight?