A federal judge in Wisconsin put one of the few remaining constraints on political spending on the endangered list this week, ruling that candidates are free to coordinate their “issue advocacy” with political action committees and other ostensibly outside groups.

Though the ruling was quickly appealed, campaign finance reform advocates said it could allow outside groups to circumvent campaign spending limits and pump money from anonymous donors into state campaigns.

The opinion by District Judge Rudolph Randa “lifts the lid off of coordination rules, and essentially ends any separation between candidates and outside groups,” said Jay Heck, executive director of Common Cause Wisconsin.

Randa ruled that Wisconsin Gov. Scott Walker and conservative groups that opposed attempts to force him from office in 2012 had a constitutional right to coordinate their efforts, including cooperating on fundraising appeals. State law can only regulate ads in which the groups engage in “express advocacy,” directly urging the election or defeat of a specific candidate, the judge said.

The judge ordered an immediate halt to a “John Doe” investigation of suspected coordination between Walker and conservative groups during the recall campaign. He said evidence gathered by prosecutors in the probe must be returned to its owners and copies must be destroyed.

If it stands, Randa’s decision would allow outside groups and candidates to sidestep individual campaign contribution limits, which are set at $10,000 for gubernatorial candidates, $1,000 for state Senate candidates, and $500 for state Assembly candidates.

Under Randa’s decision, a candidate could freely solicit donations to and support from outside groups. The groups would not contribute the money they raised directly to the candidate, but would use it to air ads or organize supporters based on the candidate’s request, and therefore may not have to disclose the spending to the public.

Randa’s ruling says that such coordination between candidates and outside groups is not “quid pro quo corruption.”

Taking another leap in judicial discretion, Randa cited precedents set in Supreme Court cases, including Citizens United and McCutcheon, to explain his decision while ignoring the fact that his ruling conflicts with longstanding campaign finance rules left in place even after those decisions.

Randa also took the idea of “dark money” to a whole other level, claiming that Walker and outside groups such as Wisconsin Club for Growth have found a new way to “circumvent campaign finance laws” that cannot be condemned or restricted.” Reasserting the deceptive idea that money equals free speech, Randa called the outside groups’ dark money “political speech.”

Though the state’s investigation is being led by a bipartisan group of distinguished attorneys, Randa dismissed it as politically motivated. His order was quickly stayed — on a technicality — by the Seventh Circuit Court of Appeals in Chicago. But Randa fixed his error on Thursday and reinstated his decision to halt the investigation. The judge’s revised order did not include the provision ordering prosecutors to return or destroy the evidence they’ve gathered. More appeals are expected.