The returns are in: 2016 will be the Form 990 election

IRS Form 990
Adam Jeffery | CNBC
IRS Form 990

In September, amid his rant-gone-viral about the spuriousness of the Miss America pageant's college scholarship program, HBO's "Last Week Tonight" host John Oliver summoned a stack of IRS 990 forms.

"We've had a weird week," Oliver cracked, as he plunked down the papers on his fake news desk, indicating that it had included much time spent poring through the annual returns tax-exempt organizations must file with the IRS.

In terms of the national zeitgeist, this represented a big moment for Oliver—but also for the stack of papers.

"Who would have thought a regulatory document would play the part of a cultural touchstone?" said Jacob Harold, president of GuideStar USA, a nonprofit that currently houses the largest searchable database of the 990 forms.

Harold notes that as nonprofits become an increasingly influential sector of the economy—according to the National Center for Charitable Statistics there are presently more than 1.5 million tax-exempt organizations in the United States, comprising more than 5 percent of U.S. GDP—the Form 990 is becoming an increasingly important window into the way things work.

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And in election politics—where a flood of dark money now flows through a complex and largely obscured system of 501(c) organizations—the Form 990 has become a focal point, a document far more revelatory than the reams of paper regularly submitted to the Federal Election Commission.

On Thursday, a group of 18 left-leaning campaign finance and open government groups sent a letter to the presidents of the major news networks imploring them to amp up their coverage of outside money in politics. This came on the heels a New York Times/CBS poll that showed American voters' continued querulousness with the influence of wealthy donors on elections.

Although it's traditionally been left-leaning activists and government watchdogs who have taken up the cause of scrutinizing 990s, this election has given conservatives just as much reason to reckon.

Consider that over the last two months, the scrutiny of Hillary Clinton's presidential campaign has been focused not on her policy papers, nor even those show-stopping Benghazi emails, but instead on the 990 forms of the Clinton Foundation—and their various revelations, discrepancies and omissions.

It seems that if the American public learns nothing else from this upcoming presidential election, it will learn some accounting.

What did they file in their Form 990 and when did they file it?

"This will be the first full presidential election where there is a much better general understanding of what a 990 is," said Robert Maguire, the political nonprofits investigator for the Center for Responsive Politics.

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If Howard Baker's famous Watergate-era line—What did they know and when did they know it?—was to be updated for present election cycle, it might now read: What did they file in their Form 990 and when did they file it?

"I think it shows the giant role nonprofits are playing in our society, and the Form 990 is a window into that," said GuideStar's Harold. "We have to remember it is not a perfect window. it is a regulatory document and not a comprehensive view, so our challenge is to gain insights from the Form 990 through the one lens it offers."

Said Maguire, "It is a fascinating document to me, and there are a lot more people looking at and recognizing there is a lot of untapped information."

Conceived by the IRS in 1941, it originated as a two-page document with three yes/no questions, and throughout the decades was confined to the bailiwick of IRS auditors and nonprofit treasurers.

But since the Supreme Court's Citizens United decision in 2010, outside-spending money has begun to shift from Super PACs, which must file monthly reports with the Federal Elections Commission, to a collection of so-called social welfare organizations, which are given the 501(c)(4) designation by the Internal Revenue Code.

Such groups include Crossroads GPS, a counterpart to the Karl Rove-led Republican Super PAC, American Crossroads, as well as a number of the cogs in the Koch brothers' donor network. These organization confront far fewer transparency requirements than other political organizations, particularly when it comes to their donors.

Basically, what we know of their activities is what they are compelled to report on their 990s.


Holy grail of dark money

This effectively makes the Form 990 the holy grail of dark money—but an imperfect one at that. As a regulatory instrument, 990s simply can't keep pace with an election cycle, let alone a news cycle.

Because 990s must be filed annually, and because it is commonplace for organizations to seek and receive monthslong extensions, disclosures very often don't make their way into the public record until a year and a half after Election Day.

"The fact that these documents are so critical now is troublesome because their filing schedule is not established in such a way that they can be used to track political activity in real time," said Maguire.

In an effort to try and help the public keep pace, CNBC.com has learned that GuideStar is planning to form a sharing partnership this year with the Center for Responsive Politics, which publishes OpenSecrets.org, a website widely relied upon by campaign operatives and the political press.

"We have more [990] data, we have it faster and better structured, but they have better expertise for how that data should be analyzed," Harold said. "We hope that we have more scale than they do, and they have more expertise than we do."

Maguire thinks that although the organizations will still take long after the 2016 election cycle to explicate the influence of money in this presidential election, the collaboration could help the organizations connect the dots looking backward.

"We can use to link it up to find new groups to figure out how networks are operating, how they are getting around limits," he said.