Disturbing revelations now appearing in special counsel Robert Mueller’s "dirty dossier" investigation of President Trump bring to mind a similar case in which political differences were criminalized and partisan prosecutors spied on Americans.

Remember the notorious "John Doe" prosecutions in Wisconsin some years back? You may recall headlines from Wisconsin in September 2011 like this: " FBI Seizes Items From Home of Former Top [Gov. Scott] Walker Aide." During that shameful episode, newspaper reporters somehow knew to arrive for a dawn raid on the home of Cindy Archer. The raid damaged Archer’s reputation and produced no evidence whatsoever of wrongdoing. It occurred six months after Republican Gov. Scott Walker signed historic labor union reforms into law, and one month after multiple recall elections failed to flip the state senate to Democratic control.

That original John Doe investigation morphed into another such investigation, and I risked jail time in order to expose the abuses. And I would still sit in jail if that would erase the traumatic memories of children awakened by flak-vested, gun-toting agents. The pain on the faces of parents unable to keep their own homes safe from invasion remains seared in my mind. Who do you call when the armed invaders have badges? And how do you treat trauma when you are told to tell no one what happened?

Democratic District Attorney John Chisholm of Milwaukee launched the first John Doe investigation to battle Walker when he was Milwaukee County Executive and a candidate for governor. Later, Walker’s union reforms energized prosecutors and led to a second John Doe with a special prosecutor. These politically motivated investigations by anti-Walker government officials led to raids on at least 14 family homes, a half-dozen offices, and the seizure of 6.7 million private documents. Dozens of conservatives, in and out of the state, were spied upon, and millions of their emails were made accessible to at least 60 government officials.

The second John Doe was launched in August 2012, two months after Walker became the first governor in America to win a recall election. It took three years and $9 million of litigation to prevail in the Wisconsin Supreme Court. "It is fortunate, indeed, for every other citizen of this great state who is interested in the protection of fundamental liberties that the special prosecutor chose as his targets innocent citizens who had both the will and the means to fight the unlimited resources of an unjust prosecution," Justice Gableman wrote for the court.

The parallels to today’s "dirty dossier" investigations are striking. Compare the leaders at the Obama-era FBI to officials at Wisconsin’s Government Accountability Board, GAB, who, our litigation revealed, designed and led attacks while hiding behind the equivalent of a special prosecutor. Like the Obama-era FBI’s view of President Trump, GAB evinced deep contempt toward Walker and his supporters — or "sheeple," as one senior GAB staffer termed them. And like the FBI, GAB officials received ill-deserved reverence from the media to which they constantly leaked.

Editorial writers in Wisconsin treated GAB director Kevin Kennedy as an oracle and defended GAB to the end. But when our litigation exposed GAB’s contempt for the people and the law, Republican legislators abolished the agency.

The John Doe abusers had national ambitions. We uncovered discussions by the prosecution team strategizing ways to silence conservative critics in the media, including Sean Hannity and Charlie Sykes, as well as to dig into the private business of Jeb Bush, Karl Rove, Paul Ryan, and Newt Gingrich.

The discoveries in Wisconsin's John Doe case and the Mueller investigation teach the same lesson: Unaccountable agencies have become powerful tools that partisan cabals can use to undermine representative government.

Secret investigations are a clear threat to our democracy. Americans' freedom rests on our constitutional rights under the law. If partisan prosecutors can target citizens for their political views, we lose those rights forever.

Political fights should be settled in the political sphere and not be criminalized. The American public, not Mueller, is the proper arbiter of facts involving our president's possible involvement with the Russian government — as well as any involvement with the Russians by the Hillary Clinton campaign and the Obama administration.

Congress, not any special prosecutor, is the proper institution to serve the public's right to know about their elected leaders. If the skullduggery in Wisconsin taught me anything, it's that Mueller's secretive investigation should be terminated immediately — and the people's Congress should investigate both the Russian matters and also the FBI's long history of political attacks.

Eric O’Keefe is director of the Wisconsin Club for Growth. He co-founded Delegates Unbound to teach delegates to the 2016 Republican National Convention that they were not legally bound to vote for Donald Trump.

If you would like to write an op-ed for the Washington Examiner, please read our guidelines on submissions here.