It makes for good political theater to frame Walker as the damsel in distress, being picked on for purely political purposes by the Democrats of Milwaukee County DA's office, but it simply isn't true.
First of all, this John Doe investigation was authorized by the nonpartisan Government Accounatibility Board (GAB), not the Milwaukee County DA. The chair of the GAB at the time the investigation was authorized, was David Deininger-- a longtime Republican member of the Wisconsin Assembly that became a judge when he was appointed by Republican Governor Tommy Thompson to the Fourth District Court of Appeals. (Deininger's actions to approve the investigation would later cost him his job in a Nixonian move to get him off of the GAB.)
Second, the person that is in leading the investigation--Francis Schmitz-- is also a Republican that has even admitted to voting for Walker in the last election. Schmitz is working with five district attorney across the state-- including two Republicans: Columbia County DA, Jane Kowley and Dodge County DA Kurt Klomburg.
Yes, Schmitz is also working with the Milwaukee County DA's office and yes they are led by a Democrat. But, keep in mind that this is the same Milwaukee County DA's office that took down former Democratic Senate Majority Leader Chuck Chvala only a few years ago. It's also the same DA's office that tried to take down Milwaukee Democrat Johnny Thomas in 2012. The notion that these guys are partisan hacks just isn't true.
So, the next time you hear someone claim this is all just a partisan affair-- agree with them.