Protesters in Washington, DC, in Dark Money (PBS Distribution)

Filmmaker Kimberly Reed takes a deep dive into the labyrinth of undisclosed, unlimited corporate spending gushing through nonprofit organizations in her home state of Montana. Both Republican and Democratic candidates there have been the subject of scurrilous and ultimately successful attacks by cryptic political action groups. In one example, a state senator was compared to serial killer John Wayne Gacy in a flyer mailed three days before Election Day, paid for by the previously unknown group Mothers Against Child Predators.

Reed traces the machinations within Montana, which is more than once referred to as a “microcosm” for spearheading campaign finance reform. Montana enacted reform as early as 1912, and in 2011, the sparsely populated state challenged the Supreme Court’s 2010 ruling of Citizens United v. the Federal Election Commission, which allowed corporations to spend freely come election time as an expression of free speech.

The film’s worldview is not limited to Montana, but includes Wisconsin’s court system, as well as the Federal Election Commission, a six-person regulating committee consisting of three members from each major political party. As pointed by out by its former chairwoman Ann S. Ravel, guidelines and resolutions have fallen by the wayside as the committee continually deadlocks in a three-to-three tie. Currently, contributions can come from foreign sources, and the amount they contribute is unregulated. The film doesn’t mention Robert S. Mueller’s ongoing investigation into Russian interference of the 2016 presidential election; it doesn’t have to.

The film also emphasizes the importance of the fourth estate, namely the diminishing breed of investigative journalists. Reed’s camera trails behind the dogged John S. Adams, whose work is indispensable to her film. Formerly at the Great Falls Tribune, Adams has founded the nonprofit news outlet, the Montana Free Press. He follows the paper trail that link a high-profile Montana politico, Art Wittich, coordinating with donors. Not limiting the debate to one side, Reed includes Jim Brown of the conservative American Tradition Partnership, one of the nonprofit groups in question, who calmly defends the Citizens United decision. If he’s an ideologue, he’s one with a sense of humor and without venom.

The litany of talking-head interviews at times threatens to turn the alarming subject matter into dry material, even with a wild tale about incriminating records found in a meth house. (Those interviewed include Democratic Senator Jon Tester, who’s up for reelection and has been a target of President Trump’s ire.) Through it all, the documentary and its time line are always lucid and detailed. Reed’s investigation becomes an inadvertent sequel to Merchants of Doubt, which emphasizes how corporate big money has influenced politics through lobbying groups, by way of Big Tobacco.

The wide screen shots of Big Sky country, including deer frolicking in front of the state capital, momentarily lift the film out of its just-the-facts approach. Viewers shouldn’t be surprised that this informative exposé will soon be headed to PBS.