Suspense is building as the midterm elections near, with control of the House and Senate—and possibly the fate of American democracy—hanging in the balance. The outcome remains unclear but one race is hardly in doubt: In the contest to influence election results, “dark money” is winning.

Kimberly Reed’s film Dark Money, nominated as best documentary for the IDA Awards and the Critics’ Choice Documentary Awards, explores the way untraceable cash from anonymous donors—corporations and wealthy individuals—is being deployed to sway voters.

“This is really about disclosure, about where this money is coming from,” Reed tells Deadline. “Because if you turn the lights off all the sudden this money starts getting used for lots of nefarious purposes.”

Some of those nefarious purposes include bankrolling attack ads and direct-mail campaigns, the kind that jam everybody’s mailboxes around election time. Dark Money details how one Republican candidate for statewide office in Montana, John Ward, got smeared with a direct-mail postcard that essentially claimed he supported child molesters.

“This was a whole new genre of political attack to shock the public right at the last moment,” Ward recalls in the film, “to leave them like, ‘We don’t want to take a chance on this guy.’”

The mailing came from conservative interests acting through a shadowy front group. In the film, investigative journalist John S. Adams uses a whiteboard to sketch how the system works: “Corporation funnels money to a dark money group. They send out postcards attacking the opponent. When [their preferred] candidate gets elected they support the agenda of the corporation.”

“The dark money that slides around…I have no doubt at all that that is happening as we speak, leading up to the midterm elections,” Reed maintains. “We should know, as voters, who’s spending money to support or oppose these candidates, and what they’re in it for, what their motivations are, what their profit motive is. Because armed with that, voters can determine whether or not there’s corruption involved.”

The director, a native of Montana, focuses much of Dark Money on her home state because of its long history with campaign finance laws. More than a century ago, state politics were controlled by mining companies, until citizens rebelled.

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“Montana’s been through it in ways that other states haven’t,” Reed observes. “I hope the other states can learn from the example of what happened [there] and see how crucial it is for voters to pay attention and to have just a modicum of media literacy when it comes to these issues so they can be skeptical of that ad they see on television, or the flyer that arrives in their mailbox.”

The Supreme Court’s controversial Citizens United decision, which ruled corporations have free speech rights, did not prohibit Congress from requiring companies to disclose their campaign spending. But the U.S. Congress hasn’t passed any such legislation, leaving Montana, for one, to fill the void.

“In Montana…this group of Republicans worked with a Democratic governor in a state that Trump took by 20 points to create some of the strongest campaign finance laws in the country,” Reed notes. “And that’s a really hopeful story, that you can have reform in this really absolutely crucial system at the heart of our democracy.”

Dark Money is now streaming on Amazon, after qualifying for Oscar consideration with a theatrical release over the summer. Lest anyone doubt the importance of the issue documented in the film, Reed cites recent history.

“Dark money played a big role in the Kavanaugh nomination for the U.S. Supreme Court, actually played it on both sides—supporting and opposing his nomination. There was much, much more money spent supporting his nomination,” the director contends. “We’re sure it played an enormous role in selecting a U.S. Supreme Court Justice for a lifetime appointment.”

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Reed is clear about which party she believes bears more responsibility for gaming the current system.

“Democrats and Republicans both benefit from dark money, in federal, state, municipal races…But I don’t want to create a false equivalency here. Because no matter what level you look at, the vast majority of that dark money is spent by Republicans,” she asserts. “And equally importantly the intent to destroy enforcement with the IRS, with the SEC, with the FEC…is very clearly tied to one political party and that’s the Republican party.”

But Reed cautions Democrats against acting holier-than-thou.

“It’s important for people on the left not just to point at Republicans and make sure that they’re the evil ones and kind of rest on the laurels as the ones who aren’t engaging in this sort of spending,” she says. “And it’s important for people on the left to vote on this issue, demand reform from their elected officials and make sure they hold their promises.”