U.S. District Judge Rudolph T. Randa, revolted by the police-state arrogance of some elected prosecutors, has stopped a partisan abuse of law enforcement that was masquerading as political hygiene. Last Tuesday, Randa halted the corruption being committed by people pretending to administer campaign regulations — regulations ostensibly enacted to prevent corruption or the appearance thereof. The prosecutors’ cynical manipulation of Wisconsin’s campaign laws is more than the mere appearance of corruption.

Eric O’Keefe’s refusal to be intimidated by lawless law enforcement officials produced Randa’s remarkably emphatic ruling against an especially egregious example of Democrats using government power to suppress conservatives’ political speech.

Wisconsin’s sordid episode began, appropriately, with a sound of tyranny — fists pounding on the doors of private citizens in pre-dawn raids. While sheriff’s deputies used floodlights to illuminate the citizens’ homes, armed raiders seized documents, computers, cellphones and other devices.

As a director of Wisconsin Club for Growth, which advocates limited government, O’Keefe had participated in his state’s 2012 debate surrounding attempts by Democrats and state and national government-employee unions to recall Gov. Scott Walker (R) and some state senators. The recalls were intended as punishment for legislation limiting the unions’ collective bargaining rights.

Walker prevailed. The Democratic prosecutors, however, seeking to cripple his 2014 reelection campaign and to damage him as a potential 2016 presidential aspirant, have resorted to a sinister Wisconsin process called a “John Doe investigation.” It has focused on the activities of O’Keefe and 28 other conservative individuals or organizations .

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In such investigations, prosecutors can promiscuously issue subpoenas and conduct searches. The identities of the targets are kept secret, and the targets are silenced by gag orders, thereby preventing public discussion of the process. Thus John Doe investigations are effective government instruments of disruption and intimidation.

Randa correctly concluded that the John Doe investigation had no reasonable expectation of obtaining a conviction. But its aim, which had been achieved until Randa’s ruling, was utterly unrelated to law. It was abetted by selective leaks by the prosecutors and by subpoenas sent to conservative donors and organizations nationwide. The purpose of all this was to suppress conservative political advocacy by consuming the time and other resources of conservative leaders, and by making people wary of collaborating with those targeted by a secretive criminal investigation.

O’Keefe and the other harassed conservatives had engaged only in issue advocacy, not express advocacy. That is, they had not urged the election of specific candidates. The U.S. Supreme Court has held that government regulation of political speech is permissible only to prevent quid pro quo corruption — money purchasing political favors — resulting from express advocacy . Hence there is no justification for the prosecutors’ punitive investigation of O’Keefe’s and others’ issue advocacy. As Randa said, this has no “taint of quid pro quo corruption” and thus “is not subject to regulation.”

The Democratic prosecutors must know this. Again, they ignore it because their aim is mayhem, not law enforcement. Their activity is entirely about suffocating conservative activity. Because the prosecutors know Wisconsin law, they are patently disingenuous in arguing that O’Keefe and others illegally “coordinated” their advocacy with Walker and other candidates or campaigns. Randa said “the record seems to validate” the denials of coordination.

Besides, and even more importantly, Randa said his court “need not make that type of factual finding.” Wisconsin law forbids coordination between third-party groups, such as O’Keefe’s, and candidates only for express advocacy , and Randa said “it is undisputed” that O’Keefe and his group engaged only in issue advocacy. The prosecutors’ indifference to this is their corruption.

Liberals inveighing against “dark money” in politics mean money contributed anonymously to finance political advocacy. Donors’ anonymity thwarts liberals’ efforts to injure the livelihoods of identifiable conservatives by punishing them for their political participation and thereby deterring others from participating.

O’Keefe’s persecution illustrates the problem his lawyer David Rivkin calls “dark power” — government power wielded secretively for vengeance and intimidation. Judge Randa quoted the Supreme Court’s 2010 Citizens United decision: The First Amendment is “premised on mistrust of governmental power.” And he noted that “the danger always exists that the high purpose of campaign regulation and its enforcement may conceal self-interest.”

Randa is insufficiently mistrustful. Campaign regulation, although invariably swathed in lofty rhetoric, is designed to disguise regulation’s low purpose, which is to handicap political rivals. If Wisconsin is serious about eliminating political corruption, it can begin by eliminating corrupt prosecutors and processes, and the speech regulations that encourage both.

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