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Gov. Scott Walker was dealt a major blow Wednesday when a federal appeals court overturned a lower court’s ruling that had stopped a probe into alleged illegal campaign activity involving Walker’s campaign and more than two dozen Republican and conservative groups.

The three-judge panel of the 7th U.S. Circuit Court of Appeals in Chicago also ordered a lower court to throw out the lawsuit, filed in February by Wisconsin Club for Growth and its director, Eric O’Keefe. Walker was not a party to the lawsuit.

The judges found that U.S. District Judge Rudolph Randa had abused his discretion and that the legality of the type of activity under investigation — coordination between ostensibly independent political groups and Walker’s campaign — “is subject to lively debate among judges and academic analysts.”

The question of whether the so-called “John Doe” investigation is allowed to continue heads back to the state Court of Appeals and state Supreme Court, which have also been asked to intervene.

O’Keefe and Club for Growth had sued in U.S. District Court in Milwaukee seeking to halt the investigation, which they alleged was a violation of their free-speech rights. In May, Randa sided with the plaintiffs and shut down the investigation.