Kennedy beat Nixon in their first debate. The truth is many people heard the debate on radio and thought Nixon cleaned up. And many researchers who study the transcripts today regard this debate as a tie on the merits. Nixon lost on television because he looked bedraggled and vaguely sinister. He had a case of the flu, and foolishly declined to shave or use TV make-up.
Debates are about image.
In an interview for PBS anchorman Jim Lehrer's show on the history of debates, George Bush the Elder says it's ridiculous to judge a leader's overall ability on his performance in a televised argument. He's probably right. What the professional politicians want their candidate to win is the battle of the sound bites, those 15-second quotes that can be easily cut for TV and radio newscasts and newspaper headlines. Voters who didn't bother to watch the debate are often heavily influenced by the coverage in the 24 hours after the debate. Debates produce great wit.