Introduction

On Tuesday, a pro-Hillary Clinton super PAC sent campaign regulators a seemingly perfunctory letter, all of 30 words long.

“This letter serves to officially notify the Federal Election Commission that Priorities USA Action will file its reports on a monthly basis to the Commission as of January 1, 2016,” it read.

Sounds harmless enough. But that little note — and more just like it from other super PACs — allows top presidential bankrollers to remain hidden as the campaign grows white hot.

That’s because, thanks to a quirk in federal law, such letters give those super PACs the power to withhold their January donors’ names until well after the first-in-the-nation Iowa caucuses and New Hampshire primaries are conducted next month.

Also secret: the potentially massive amounts of money the donors are contributing in order to affect the outcome of those crucial contests.

Instead, the super PACs will file campaign finance disclosure reports that only include contributions they’ve received through December.

Beyond Priorities USA Action, 10 other presidential super PACs have so far taken advantage of this opportunity to withhold information about their January donors, a Center for Public Integrity review of federal records indicates.

They include:

“The situation is really inappropriate — the whole point of disclosure is to provide information to voters when they need it,” said Ann Ravel, a Democratic member of the Federal Election Commission who served as the agency’s chairwoman last year.

Ravel, however, acknowledged there’s little the FEC can do about it at this juncture, and current FEC Chairman Matthew Petersen concurred.

Lee Goodman, a Republican FEC commissioner, noted that political action committees commonly change their filing status during election years to put themselves on a predictable, monthly schedule. Otherwise, they’d be forced to file campaign finance disclosures before every primary contest in which they participated — an onerous prospect.

“I don’t think they’re doing this for subterfuge, and I’ve never heard of a voter who based his or her vote on the identity of a donor to a super PAC,” Goodman said. “But this does, perhaps, leave a gap in disclosure, which is important and certainly something the commission could look at.”

Here’s how the super PAC filing loophole works:

Most major super PACs filed just one campaign finance disclosure report during 2015, as the law allows them to do.

But this month, these “semi-annual” super PAC filers who’ve spent money in the New Hampshire primary campaign race face a choice.

They may choose to do nothing, maintain their current status and be required to submit a “pre-primary” report on Jan. 28 — 12 days before New Hampshire’s Feb. 9 primary.

Such a pre-primary report would reveal everyone who’s given a super PAC money — and how much — through Jan. 20. (Because of a 36-year-old FEC ruling, presidential caucus contests such as the one Iowa conducts on Feb. 1 don’t trigger such reports.)

Or, as many super PACs already have, they may this month notify the FEC that they’re switching to a monthly filing schedule.

Doing so exempts a super PAC from filing Jan. 28 pre-primary reports, and therefore, revealing their income from Jan. 1 through Jan. 20.

Instead, they’ll file a report disclosing their 2015 fundraising on Jan. 31 and another report detailing their January fundraising on Feb. 20, per FEC rules.

Some presidential race-focused super PACs pulled a similar donor-hiding switcheroo ahead of the 2012 election, although this time around, super PACs are raising exponentially more money to promote their candidates of choice — or lambaste those they oppose.

Technically, the FEC could deny such filing change requests. But the agency almost never does.

Pro-Clinton Priorities USA Action spokesman Justin Barasky declined to comment on the super PAC’s switch, as did pro-Bush Right to Rise USA spokesman Paul Lindsay.

None of the other presidential super PACs who’ve switched their filing status responded to requests for comment from the Center for Public Integrity.

One person who’s steamed about the situation is Sen. Bernie Sanders of Vermont, who’s emerged as Clinton’s strong primary rival while disavowing all super PACs.

“I’m shocked,” Sanders spokesman Michael Briggs said when told of the pro-Clinton Priorities USA Action filing switch. “You’ve got to ask the question, ‘What are they afraid of?’”

The Supreme Court’s 2010 decision in Citizens Untied v. Federal Election Commission helped lead to the initial creation of super PACs later that year.

Super PACs — initially exotic political vehicles that sprung into existence following Citizens United — have this election cycle evolved to become conventional weapons of most presidential efforts.

Unlike traditional PACs, which may only raise money in limited increments, super PACs may raise and spent unlimited amounts of money to advocate for or against political candidates — so long as they don’t directly coordinate messaging with a candidate’s campaign.

Together, super PACs have raised hundreds of millions of dollars to support White House hopefuls, and before Election Day in November, they’ll assuredly raise hundreds of millions of dollars more.

Dozens of individuals had already given super PACs at least $1 million by June 30, when such groups were last require to report their income.

University of New Hampshire political science professor Dante Scala says he doubts the revelation of some 11th-hour super PAC donor would sway most New Hampshire primary voters’ votes.

But there’s always a chance of something surprising occurring — perhaps a major Democratic donor funding blanket attack ads on a Republican, or billionaires Charles and David Koch suddenly pumping cash into some effort after month remaining neutral.

“You’d like them to err on the side of transparency,” Scala said.

This story was co-published with the Concord Monitor and Al Jazeera America.