McCain Has Left the Building

So I thought it was odd that after the debate the camera kept focusing on Obama and his wife chatting with the crowd. Why weren't they showing McCain? Well I just heard on Countdown with Keith Olbermann that McCain pretty much left as soon as the debate ended. Isn't the purpose of a town hall so candidates can interact with voters? Why wouldn't McCain want to stick around and meet them? Obama and his wife were shown shaking hands, chatting and taking pictures with voters. Even Tom Brokaw stuck around!