A great summary:
When the networks (flouting the debate rules) cut to Mr. Bush while Senator John Kerry was speaking, the president had the hunched shoulders and the peevish, defensive look of an incumbent under heavy attack.
And it was body language as much as rhetoric and one-liners that distinguished the two candidates in last night's debate. The networks were right to disregard the campaigns' ban on cutaways and reaction shots. Instead, all the networks, including Fox News, lavished viewers with split screens and shots of the candidates from almost every angle, including shots from behind the president's tensely knotted back.
The cameras demonstrated that Mr. Bush cannot hear criticism without frowning, blinking and squirming (he even sighed once). They showed that Mr. Kerry can control his anger and stay cool but that he cannot suppress his inner overeager A student, flashing a bleach-white smile and nodding hungrily at each question.
Mr. Bush, who seemed to grow tired as the night wore on, repeatedly used the phrase "hard work" to describe the war in Iraq. Mr. Kerry repeatedly referred to his first-hand experience sending men into battle in Vietnam, and that seemed to unnerve Mr. Bush. The president said he understood that fighting was hard work and added, "I see on the TV screens how hard it is."
TV debates are also hard work.
http://www.nytimes.com/2004/10/01/politics/campaign/01teevee.html