Voter disgust over political spending by corporations and unions is driving support for a Montana ballot measure to ban "dark money," potentially testing the Supreme Court's Citizens United decision. The measure has backing from a former Republican governor and a Democratic senator. The main challenge: threading the needle of the 2010 ruling that allowed independent political spending as free speech.

Supporters argue corporations are state-registered entities, so Montana can revoke registrations for political spending, making it a state sovereignty issue. Opponents, including the Republican governor and Montana Chamber of Commerce, call it unconstitutional. "I haven't talked to a person yet that doesn't think that there's too much money in politics," said Jeff Mangan, founder of the Transparent Election Initiative.

If passed in November, it would take effect Jan. 1, 2027, making Montana the first state with such a law. Hawaii approved a similar ban in May, already being challenged. In 2024, nearly $2 billion in dark money was spent nationally, per the Brennan Center for Justice.

Montana, which President Trump won by 20 percentage points in 2024, has a populist streak and distrust of big institutions. The measure would bar businesses, unions, and nonprofits from donating to candidates or parties. It requires a simple majority. Opponents say it concentrates power among wealthy individuals.