Lehrer Discusses Contours Of Presidential Debate Jim Lehrer has moderated ten presidential debates in his lifetime. But as he approaches his responsibilities as the host of the first go-around between Barack Obama and John McCain, his nerves aren't any calmer than when he first did this. "If you screw this thing up it isn't like a television program where you can say, "Oh sorry, I'll do better tomorrow. . . if you make a mistake as a moderator in one of these debates it could affect who becomes the next president of the United States." The first debate is one week from today.