The battle to control the Senate was a proving ground for the new Citizens United politics. Outside groups unleashed heavily funded barrages of attack ads meant to help elect candidates while letting them keep their distance from the nastiness.

In Ohio and Virginia, the tactic failed in rather dramatic ways, as Republicans backed by secretly financed ads failed to beat seemingly vulnerable Democrats.

Ohio State Treasurer Josh Mandel, thought to be a rising star among state Republicans, enjoyed massive support from groups based in Washington, D.C., and elsewhere. But he still couldn't topple Democratic incumbent Sherrod Brown, who got some — but significantly less — outside support from D.C.

Mandel's campaign ran about 13,000 ads on broadcast TV between the start of the general election campaign and late October, according to Kantar Media CMAG. Outside groups ran twice that many. Crossroads GPS, the social welfare organization co-founded by GOP strategist Karl Rove, spent $8.8 million on ads, about $2 million more than the candidate's campaign.

Perhaps most significant, 60 percent of the pro-Mandel ads that Ohio viewers saw on TV came from groups that keep their donors secret: social welfare organizations like Crossroads GPS and 60 Plus, and business groups, including the U.S. Chamber of Commerce. By comparison, the effort to re-elect Brown included one social welfare group, the League of Conservation Voters, which produced 889 of the 23,000 ads supporting the Ohio senator.

In the Virginia Senate race, George Allen, a former governor and senator, depended on outside groups even more than Mandel. The campaign of Allen, a Republican trying to reclaim his seat, spent about $3 million, according to Kantar, to run barely 4,500 ads of his own.

The big advertiser for Allen: Crossroads GPS again, spending more than $9 million.

In all, groups spent $20.6 million advertising for Allen. Of that, 57 percent was given by secret donors to Crossroads GPS, the U.S. Chamber of Commerce and other nondisclosing groups.

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