Chalk up a big victory for the First Amendment. On Friday a Wisconsin judge struck a major blow for free political speech when he quashed subpoenas to conservative groups and ordered the return of property to the targets of a so-called John Doe campaign-finance probe.

John Doe probes operate much like grand juries, allowing prosecutors to issue subpoenas and conduct searches while gag orders require the targets to keep quiet. We wrote about the kitchen-sink subpoenas and morning raids by special prosecutor Francis Schmitz that targeted dozens of conservative groups that participated in the battle to recall Republican Governor Scott Walker ("Wisconsin Political Speech Raid," Nov. 16, 2013).

Now we learn that Judge Gregory A. Peterson ruled on Friday that at least some of those subpoenas were improper. They "do not show probable cause that the moving parties committed any violations of the campaign finance laws," he wrote. His opinion remains under seal but we obtained a copy.

The quashed subpoenas were sent to Friends of Scott Walker, Wisconsin Manufacturers & Commerce Inc., the Wisconsin Club for Growth, and Citizens for a Strong America, as well as their officers and directors. Judge Peterson's order doesn't apply to other subpoena targets, but they can presumably get the same result if they file a motion with the judge and have a similar factual basis.

The order is all the more remarkable because it bluntly rejects the prosecutor's theory of illegal coordination between the groups and the Walker campaign. Wisconsin's campaign finance statutes ban coordination between independent groups and candidates for a "political purpose." But a political purpose "requires express advocacy," the judge wrote, and express advocacy means directly advocating the election or defeat of a candidate.