Of course. We all know that to be the case. The MSM's bias is undeniable.
But the thing is that they can't label the guy as a "Democrat" or as a "Republican" if he wasn't elected as such. The mayor of Nashville is pretty liberal, and I have little doubt that he pulls the donkey when he's in the voting booth, but he was not elected "Karl Dean - D;" he was just elected "Karl Dean."
For some reason, "pull the donkey" sounds more like what the guy in the OP was doing than voting for Democrats.