I have no idea if Wisconsin Gov. Scott Walker is guilty of illegally coordinating his 2012 campaign against a recall with outside groups, as Wisconsin prosecutors have accused him of doing in documents just released by a federal appeals court. He denies it. Nor do I know if Walker is actually dumb enough to have sent this email, included in the released documents, to Republican strategist Karl Rove—an email that explains how one of Walker’s main deputies would be the point person coordinating activity between Walker’s campaign and a network of outside conservative and business organizations headed by the Wisconsin Club for Growth.

Walker hasn’t been charged, and a judge stopped the prosecutors from further investigating last month, a ruling that is now on appeal. That ruling should be reversed, because the main defense against the state prosecution is one that, if successful, could bring down the few remaining limits we have left on money in politics. It would allow virtually unbridled coordination between outside groups and candidates, giving money ever more influence over politicians and elections.

In the election law business, the distinction between “independent” and “coordinated” spending is kind of like the line between church and state in the U.S. Constitution—seemingly impenetrable, but subject to all sorts of exceptions and quirks. Independent spending is spending on election activities done without touching base with a candidate and her team. Coordinated spending involves spending in cooperation or consultation with a candidate. The suit to quash the Walker investigation would obliterate the line between independence and coordination, effectively lifting the remaining contribution limits to candidates.

According to the Supreme Court in the 2010 case Citizens United v. FEC, it is constitutional for the government to limit direct contributions to candidates to prevent corruption or the appearance of corruption. But it is unconstitutional to limit spending that goes to “independent” groups that support or oppose candidates. The court held that independent spending can neither corrupt nor create the appearance of corruption. That’s a controversial notion, but you can put it aside for now, because it’s not at issue in the Walker case. Focus instead on the question of what counts as “independent” spending as opposed to spending that is coordinated.

Both federal law and Wisconsin law have rules to decide what counts as illegal “coordination,” and the legal definition is much narrower than the standard definition of that word. Under federal law, for example, a candidate can appear at a fundraiser for an outside group without “coordinating” with it. The candidate and her campaign merely cannot talk about ad buys or campaign strategy. If a candidate and an outside group engage in this form of coordination, then the amount spent is subject to limits.

State prosecutors secretly investigated Walker to figure out if he and his team were illegally coordinating with outside groups and nonprofits that worked against his 2012 recall. At the center of the investigation, we know, was the Wisconsin Club for Growth. The group sued in federal court to shut down the investigation, which it said violated its First Amendment rights to engage in political activity. The suit thus advanced a claim well beyond the constitutional right to spend money independently.

The Club for Growth did not deny coordinating its strategy with the Walker campaign. The group served as a hub for directing money to a host of groups running ads supporting Walker. Still, the club argued that its activities were legal because it simply coordinated a run of “issue ads” on the question of the Walker recall, which mention a candidate for office but don’t include the magic words “vote for Walker” or in this case “vote no on recall.”

Issue ads were a common way to avoid campaign finance restrictions before Congress passed the 2002 McCain-Feingold law. A famous issue ad accused Montana Democratic candidate Bill Yellowtail of taking a swing at his wife and implored voters to “Call Bill Yellowtail. Tell him to support family values.” Because the ad didn’t include those magic words of advocacy, the donations that paid for it didn’t even have to be disclosed: They weren’t treated as real election ads.

The McCain-Feingold law sought to put an end to that kind of runaround. The reform treated issue ads broadcast on TV or radio in the 30 days before a primary, or 60 days before a general election, the same as ads containing the magic words of “vote for” or “vote against.” Part of that provision of McCain-Feingold—the limit on corporate and union spending on issue ads—died in Citizens United. But the federal rules about disclosure still govern for issue ads, meaning that at least the public knows who is paying for them. The Federal Election Commission also counts issue ads as relevant in determining when a candidate and outside groups are illegally coordinating. Run certain issue ads about a candidate before an election in cooperation with a candidate and you’ve crossed the legal line.

Yet somehow, in the Walker case, federal Judge Rudolph T. Randa agreed with the Club for Growth that coordinating issue ads is perfectly OK. The opinion drips with hyperbole. “Attempts to purify the public square lead to places like the Guillotine and the Gulag,” Randa wrote. Also, “The plaintiffs have found a way to circumvent campaign finance laws, and that circumvention should not and cannot be condemned or restricted. Instead, it should be recognized as promoting political speech, an activity that is ‘ingrained in our culture.’ ” And with that, Randa ordered an end to the investigation and, incredibly, given that the case is only at a preliminary stage, ordered the destruction of all the evidence.

Randa’s indefensible move to destroy evidence got the attention of the United States Court of Appeals for the 7th Circuit, which put his order on hold. The 7th Circuit also allowed Thursday for the release of the documents setting out the prosecutors’ evidence.

If Randa’s ruling stands on appeal, then the rules against coordination between a candidate and outside groups would go out the window in Wisconsin. That would be license for big donors to give unlimited sums to groups that will do candidates’ bidding. According to the Huffington Post, the Wisconsin Club for Growth pulled in $20 million during 2011 and 2012, much of it from business and industry groups, including the controversial Koch brothers. The club then doled out the money to other groups, with some of it, for example, ending up in the hands of Wisconsin Right to Life, which could then run issue ads about the recall targeted at its abortion-opponent constituency. It all made a Big Business effort, paid for with Big Business money, look appealingly grassroots.

So that’s the future if Judge Randa’s ruling stands—big money being raised and channeled, in cooperation with a candidate to the benefit of that candidate, obliterating the line between independent and coordinated spending. There’s a good chance the 7th Circuit will disagree with Judge Randa and hold the line against this. But here’s a more alarming scenario: The case winds up at the Supreme Court. The conservative majority of justices has struck down campaign finance limit after limit. Who knows what they would do with the coordination rules? The only way to win on campaign finance before the Roberts court is not to play.