Congressional Democrats have a higher net favorability rating than Congressional Republicans by about 10%. Meanwhile, Republicans are beating Democrats in the generic ballot by 5%. (My sense is that the generic ballot is the one to use to predict the 2010 election. It's a ballot!) This makes a straightforward kind of sense, I suppose, because Democratic control means that most races have a congressional Democrat against a Republican challenger. So is this just an issue of anti-incumbent sentiment? I'd be surprised if that was the sole cause of such a big difference.