Political junkies will feel their blood boil watching this new documentary

Investigative journalist John S. Adams, seen in the Montana Capitol building, is the guide through the thicket of issues explored in the documentary “Dark Money.” (PBS Distribution/Big Sky Film Productions)

Rating: 2.5 stars

Citizens United , the 2010 Supreme Court case in which corporations and labor unions were determined to have the same free-speech rights as individuals, has cast a long shadow over U.S. elections — and U.S. documentary filmmaking.

In movies such as “Citizen Koch” and “Pay 2 Play,” the idea of “corporate personhood” — the notion that businesses are, in a sense, people — is shown to have paved the way for moneyed groups to buy ads attacking politicians who stand in the way of their interests. Hiding behind advocacy organizations with vague, patriotic-sounding names, firms are given free rein to funnel money anonymously — money that they are otherwise legally barred from contributing directly to a campaign — to middlemen who can run the kind of partisan advertising “where you don’t know who’s paying for the ads.”

That’s the description of the problem offered up in “Dark Money,” the latest documentary to explore the influence of corporate cash on elections. Set in Montana, the home state of filmmaker Kimberly Reed, this well-made, Sundance-nominated film tells its story through the eyes of journalist John S. Adams, a former investigative reporter for the Great Falls Tribune who now runs the muckraking website Montana Free Press.

What’s so special about Montana?

The state, long known as a bastion of independent spirit, was the only one to fight back against Citizens United, leading to its own Supreme Court battle. Using Adams as a guide of sorts — supplemented by interviews with such subjects as Sen. Jon Tester (D-Mont.), former Federal Election Commissioner Ann Ravel, CNN legal analyst Jeffrey Toobin and the attorney for one of those patriotic-sounding groups, Jim Brown, who represents American Tradition Partnership — “Dark Money” takes a deep dive into a subject that will either bore you to death or boil your blood. As a Washington political junkie, I fall into the latter camp. Your results may vary.

Fortunately, Adams makes for an engaging sherpa in this weighty endeavor, translating much of the film’s heaviest concepts into easily understandable parcels — in one case, via a simple diagram on whiteboard. No expensive graphics or digital animations for Reed, a filmmaker who, despite a penchant for bare-bones filmmaking, nevertheless makes her argument clearly and convincingly.

And why should Washingtonians — or anyone outside of Montana, for that matter — care about that argument? Because, as Ravel puts it, the disproportionate influence of money on elections isn’t a Democratic or Republican problem, but a “gateway issue to every other issue you might care about.” “Dark Money” makes the case, as well as any film can, that she’s pretty much right on the money.

Unrated. At Landmark’s E Street Cinema. Contains some strong language. 98 minutes.

The theater will host Q&As with director Kimberly Reed following Friday’s 7:30 p.m. show and Saturday’s 1:30 p.m. show.