A new Center for Responsive Politics report uncovers some more details about the money behind American Crossroads, one of the most powerful right-wing spenders in the 2010 elections.

The Karl-Rove founded group acted as a “Shadow RNC” in this year’s elections, collecting and distributing money from wealthy donors who were shying away from the embattled party committee. But it also had a brand new leg up: the Supreme Court’s decision earlier this year to allow corporations to spend unlimited amounts of money on influencing elections. A full third of American Crossroad’s $28 million in funding came from corporate donors, CRP found. And a big chunk of American Crossroad’s remaining cash—54%–came from just four wealthy donors.

And that’s just the branch of American Crossroads whose funding we know about. The group’s sister organization, Crossroads GPS, spent $17 million on elections, and according to CRP,” saw its preferred candidates win in 71 percent of the races in which it invested money.” We can’t know for sure about the sources of GPS’s funding, since it doesn’t have to report its activities to the Federal Election Commission, but we do know that it received significant funding from Wall Street bankers. Once source told Politico in October that “most of the GOP corporate money is believed to be moving through [Crossroads GPS], so that it isn’t disclosed publicly.”

Rove himself has said that the Citizens United decision made the success of American Crossroads and American Crossroads GPS possible. In turn, his groups helped to define what political spending looks like in the post-Citizens United era, where corporations and a few wealthy individuals have enormous power over elections—but rarely have to own up to it.

 UPDATE: Mother Jones has more on the Big Four donors to Crossroads.