Half of the Senate faces the voters in November. It's expected that the Republicans will pick up at least two Senate seats at that time. By November the new legislative districts will be in use. These were drawn by the majority Republicans in 2011 and are tilted in the GOP's favor.
Lol! The money lines! It would almost be worth it to see the democrats take control of the Senate, then realize that they haven't actually won anything because there will be another election which the Republicans will most likely win before the Senate is back in session.
More importantly, in November the Voter ID requirement will be in effect, and vote fraud will be a bit harder. The most important part is to keep Gov Walker, because the effectiveness of Voter ID depends on state willingness to enforce.