I would imagine Janesville is heavily Dem, but leans private union as opposed to public. There was a GM plant there, now closed. People are hurting and I think they are probably open to giving Walker’s policies a chance since Hopenchange hasn’t done a lot for them thus far.
Also note that its Paul Ryan’s home district too. This is an area that is filled with “Reagan Democrats” that suffered through the debacle otherwise known as the Diamond Jim Doyle Governorship.