This Washington Post article by Terry Neal makes a good point:

In the weeks and days leading up to tonight’s debate, every pundit has had an opinion on what the candidates needed to do in the debates. For Kerry, the conventional wisdom was that he needed to prove that he was not a flip-flopper and enunciate a clear vision on the important issues of the day.

True enough. But the biggest hump for Kerry to get over tonight is the likeability hump. Kerry needs to prove that he is not the officious, stentorian bore peddling snooze-inducing and confusing bromides, as his Republican opponents have worked so hard to portray him.

This is not to say issues don’t matter. They do. But the Bush attacks on Kerry have been devastatingly effective because even the issues campaign has been based on personality and character issues. Has Bush -- who continues to get sub-50 percent ratings on his handling of Iraq and the economy -- moved ahead of Kerry in the polls because he has articulated better positions on the biggest issues, or because he has convinced people that the flip-flopping Kerry will say whatever’s politically expedient at the moment?

Yep. The hardcore left is so venomously anti-Bush that they figure any old rag doll will do when thrown up against him. But I think Neal's right that the undecideds are going to decide based in great part on their gut reaction to the guy. And Kerry is just not likeable. Bush is. This is hard for those who see Bush as a Retarded Chimp Cowboy Hitler, but to your average person Bush comes across as much more relaxed, confident, and friendly than Kerry.

I thought Kerry did a good job on The Daily Show at seeming more human, but I've seen enough other appearances where he comes across as a haggard, droning, humorless windbag to form a reasonably unenthusiastic view of the guy.

Kerry's going to have to appear more plain-spoken and likeable if he's going to have a snowball's chance in this election.