The pundits say that only the independent and undecided voters are swayed by the debates. However, if one of the candidates comes out of who knows where with some idea, he may lose or gain support, depending on how smart or how ridiculous the idea may have been.
Presidential elections are kind of like baseball. It is not over until the last batter is out. In baseball, a team can be down 10 to Zero in the bottom of the ninth and make a rally to win. In Presidential elections, one candidate can be far ahead, or they can be necked and neck. It is not over until the last speech has been made, and the last questions answered. Granted, elections are more predictable than baseball, but the principle is the same.