ONE corner of the world of “dark money” just got a little brighter, and it doesn’t bode well for the 2016 election.

A recent tax filing by Carolina Rising, a 501(c)(4) social welfare organization, shows that in 2014 the group spent $4.7 million on ads that had one thing in common: touting the legislative accomplishments of Thom Tillis, who was then North Carolina’s speaker of the House. That year, Mr. Tillis also happened to be trying to unseat Kay Hagan, the incumbent Democratic senator.

Carolina Rising spent the money in a three-month blitz leading up to Election Day, but we may never learn where these millions came from. The partial disclosure required of 501(c)(4) outfits means that while we do know that 98.7 percent of the group’s revenue came from a single donor and that virtually every penny of it was used to further the cause of Mr. Tillis’s campaign, we don’t know who Carolina Rising’s secret benefactor was.

John Koskinen, the I.R.S. commissioner, is scheduled to testify today before the Senate Finance Committee at yet another hearing on the agency’s heightened scrutiny of certain politically active 501(c)(4) groups in 2010-12. But what we should really be paying attention to is the increasing use of dark money to influence our elections, and the rising number of groups that devote themselves to a single candidate (including several, already, in this cycle’s presidential campaign). Before the 2014 campaign, nonprofits like that didn’t exist.