In the midterm elections this year, tens of millions of dollars flowed from secret donors into pivotal races through nonprofits. We may never know who really paid for the election of a whole new class of politicians.

Here’s a hint of where the money might be coming from: the lobbyists who control the gusher of money.

Crossroads GPS and the American Action Network, according to filings, were two of the largest dark money groups in America. Both are organized under the 501c4 section of the tax code, meaning they do not have to disclose a dime of donor money.

Here’s another similarity: both are led by lobbyists for Sallie Mae, the nation’s largest student loan servicer.

— Sally Vastola, a lobbyist at the law firm Nixon Peabody, is on the board of Crossroads GPS. Her disclosures show that she works on debt collection issues on behalf of Sallie Mae.

— Vin Weber, a former congressman from Minnesota, now leads the American Action Network as a member of its board of directors. But his day job features work as a lobbyist, also serving Sallie Mae, through a firm called Mercury. Weber’s filing shows he has worked to block student loan reforms, including efforts to allow student loan debt to be discharged during bankruptcy.

Sallie Mae has seen its profits soar in recent years as student debt continues to climb. The company reportedly increased its private education loan holdings by 26 percent, and now controls around $7.8 billion worth of private college debt. Filings from the firm also show the company is closely monitoring — and likely obstructing — movement on Capitol Hill to rein in student debt. Sallie Mae has lobbied on Senator Elizabeth Warren’s bill to reduce the interest rate on government-backed student loans.

In the election this year, GPS focused primarily on Senate races — with large sums spent on defeating Mark Udall, Kay Hagan, and Mark Begich — and the American Action Network focused on increasing the GOP House majority.

Did Sallie Mae secretly fund these attack ads? Their lobbyists certainly controlled the purse strings. Sallie Mae did not respond to a request for comment.

In somewhat of an ironic twist, many of the dark money ads sponsored by GPS attacked Democrats for not doing enough on debt issues. Meanwhile, about 40 million Americans still hold student loan debt, with an average balance of $23,000.