Karl Rove, former chief political adviser to former President George W. Bush, gestures as he addresses members of the Virginia Chamber of Commerce in Williamsburg, Va., Thursday, Dec. 2, 2010. (AP Photo/Steve Helber)

Karl Rove’s Crossroads GPS is allowed to spend unlimited amounts of money on attack ads in battlegrounds states—without ever disclosing a single donor—because it has protected status as a 501(c)(4) nonprofit organization. Unlike Super PACs, which must disclose donors, Crossroads GPS and other groups don’t have to disclose because they supposedly don’t have political activity as a primary purpose, and therefore are allowed to protect their funding sources.

But this is one of the Big Lies in American politics. Of course the primary purpose of Crossroads GPS—which is run by former high-level Republican Party officials—is to influence elections. In recent months, there’s been increasing pressure on the IRS to call the bluff: Congressional Democrats wrote a letter to the agency asking it to reconsider the tax status of Crossroads GPS and other groups, and nine Republican senators quickly responded with an ominous letter to the IRS warning it not to act.

But Crossroads GPS’s decision to pull television advertising in Missouri in the wake of Republican Senate candidate Representative Todd Akin’s abhorrent comments about rape and pregnancy are (another) bold admission of why the group really exists.

Crossroads GPS is a major player in the Missouri Senate race—it has spent $5.4 million already, which more than doubles the $2.2 million spent by Akin’s actual campaign. The ads “seek to paint [Democratic candidate Claire] McCaskill as a big government-loving, tax-increasing liberal” and hit her for voting to increase the debt limit, among other things.

Under the law, Crossroads GPS and other 501(c)(4) can’t expressly advocate for or against the election of a specific candidate—it can intervene in political races “as long as its primary purpose is the promotion of social welfare” (and then no more than 50 percent of its total activities should be such interventions). Ostensibly these ads are educational—telling voters about issues at stake in a race, but not backing a particular candidate.

But after Akin made his horrific comments about “legitimate rape,” Crossroads GPS announced it was pulling all advertising. “The act speaks for itself,” Crossroads spokesman Nate Hodson said.

This obviously vitiates any argument that the ads are simply to promote social welfare—that, say, the most recent spot is simply meant to educate voters about the national debt. What has changed about McCaskill’s vote on the debt limit? Nothing. What has changed is that suddenly the Republican candidate in that race is viewed as unelectable by basically the entire political establishment—and now Crossroads doesn’t want to spend any more money there. That act speaks for itself, indeed.