It looks like there are a couple of factors here. One, the Republican convention was extremely lackluster and fairly negative. "Vote for me because Obama sucks." By contrast, the Democratic convention is getting a lot of kudos for being everything the Rs used to be -- disciplined, on message, ruthlessly upbeat and totally energizing to the party faithful. This leads to (2) Republicans getting increasingly defensive and folks like Rush getting whackier. Meanwhile, despite insistence that Obama does not have a plan, news outlets keep noting that Romney's "plan" is kinda more like a wish list with a bunch of gaps.
Mind you, things are close enough that a significant news event or a major stumble in the debates can turn things around. But you never want to have to come from behind.