If you're a Republican anywhere that pretty much all of them, as history has shown. But in Wisconsin the police and fire unions had the great good sense to support Walker and surprise, surprise they were the only two that didn't have their collective bargaining rights taken away. Now since the Democrats have pissed off the Unions with their support of the TPP and other issues then if the Unions want to protect what they have left they may as well remain neutral or go for the GOP.
I have to respectfully disagree about the fact that Wisconsin is pretty much like any state. It is the birthplace of government unions, literally, and one of the most powerful (formerly) gov union states in the nation. Now - to your point above - Walker didn't take any collective bargaining rights away - he just destroyed the mandatory dues withholding and gave teachers and other employees the choice. He couldn't have done that without winning the election, and if he needed to push the fire/police union reform to the back burner, then it was a wise decision.
Sconsin ain't Mizzou.