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If your congressman has been bought, at the very least you have a right to know who bought him. Wouldn’t you agree?

With that in mind, we’re cheering for an effort in South Dakota — conservative, sparsely populated South Dakota — to put a measure on the November ballot there that would require people and groups who throw big money into elections to put their names on their donations for all to see — no more secret or “dark” money.

If South Dakota can pull this off, despite an enormously expensive campaign against the measure by the very same people who should be pulled out of the shadows, we figure Illinois could be next. Which would be great. Nobody has ever called Illinois a model of open and transparent democracy.

The South Dakota effort, Initiated Measure 22, calls for several other political reforms as well, such as a new twist on the public financing of campaigns, but we are most enthusiastic about the provision to limit dark money. The proposed reform would put no limit on how much money a corporation or individual could spend to influence any election from dog catcher to president — a right established in the Supreme Court’s Citizens United decision of 2010 — but it would eliminate their ability to do so anonymously.

Opponents, beginning with the billionaire Koch brothers, warn this would have a “chilling effect” on political discourse, which is exactly what internet trolls say whenever a website blocks their wretched anonymous comments. We predict it would lead to a slightly more fact-based and high-minded debate.

As things go now, so many of those ugly political ads on TV, paid for by anonymous and supposedly independent supporters of this or that candidate, amount to little more than slick trollwork. How is a voter supposed to gauge the credibility of an ad in support of a candidate who favors burning more coal for fuel — just as an example — if he or she doesn’t know that the group paying for the ad gets its money from coal companies?

Prohibiting anonymity by donors in elections, the Supreme Court suggested in the Citizens United decision, is legal and can be helpful. As Justice Anthony Kennedy wrote, “Shareholders can determine whether their corporation’s political speech advances the corporation’s interest in making profits, and citizens can see whether elected officials are in the pocket of so-called money interests.”

Dark money threatens to swamp our political system. According to the watchdog group OpenSecrets.org, outside spending in federal elections by groups that do not disclose their donors has gone from just $690,000 in 2006 to $51.7 million so far in 2016. Dark money may even explain the presidential candidacies of both Sen. Bernie Sanders and Donald Trump. Supporters of both anti-establishment candidates are convinced that dark money has led to a bought-and-paid-for Congress that serves only the interests of the 1 percent.

But efforts to control dark money at the federal level have been stymied by Republicans and some Democrats in Congress who are not about to turn on their sugar daddies. The Internal Revenue Service and the Securities and Exchange Commission both have the power to require significant new campaign funding disclosure, but have done nothing.

And so it is left to reformers at the level of the states, as in South Dakota, to get something done, ideally in a bipartisan manner. Surveys shows that well over 60 percent of both Republican and Democratic voters favor more public disclosure of the source of money in elections. The organization pushing the measure in heavily Republican South Dakota is chaired by a Republican former state senator and a Democratic former state representative.

State action will never be enough. It is unclear, for example, whether a state could impose new disclosure rules on the funding sources of federal political action committees, even if the federal PACs spent money on state races.

But partly sunny beats a rainy day.

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