WASHINGTON (AP) — Nearly $5 million in advertising to help elect Republican North Carolina Sen. Thom Tillis in last year’s midterm elections came from a group that does not have to disclose its donors.

That’s according to tax filings made public on Tuesday by Crossroads GPS. That group was co-founded by Karl Rove, a strategist for former President George W. Bush.

The filings show that Crossroads gave $4.8 million to Carolina Rising, another nonprofit. That grant made up almost its entire budget.

In turn, Carolina Rising spent nearly every penny of that money on pro-Tillis television ads.

The Washington-based political watchdog Citizens for Responsibility and Ethics in Washington had complained to the Internal Revenue Service that Carolina Rising abused its nonprofit status.