The Supreme Court has an opportunity to reconsider its disastrous Citizens United decision. The justices should take it. The damaging effects of unlimited spending by corporations and unions on elections — honestly examined — should cause the court to overturn or, at the very least, limit that ruling.

On Friday, the justices granted a stay of a Montana state court ruling that upheld a state anticorruption campaign finance law. The stay gives the parties in the Montana case time to file papers to seek Supreme Court review. In supporting the stay, Justice Ruth Bader Ginsburg wrote, “Montana’s experience, and experience elsewhere since this court’s decision in Citizens United v. Federal Election Commission make it exceedingly difficult to maintain that independent expenditures by corporations ‘do not give rise to corruption or the appearance of corruption.’ ” She was quoting Justice Anthony Kennedy’s majority opinion in Citizens United, in which he claimed that expenditures might result in “influence over or access to elected officials” but would not “corrupt” them.

The Montana state court ruling rests on a careful review of the political corruption that led the state to pass its Corrupt Practices Act. The Citizens United ruling, by contrast, is based on no evidentiary record at all. The Supreme Court, on its own initiative, took up the broad question of corporate and union spending when the controversy in the case was much narrower. The court’s conservative majority essentially used the Citizens United case to overturn a century of established federal law by imposing its own legal theory, without relying on facts.

The gap between the court’s mistaken assumptions (“the appearance of influence or access, furthermore, will not cause the electorate to lose faith in our democracy”) and the real-world effect of the cash unleashed by the decision could not be more glaring.