Americans for Responsible Leadership -- one of the political nonprofits involved in a scheme last year that California authorities called political "money laundering" -- spent more than $25.2 million last year, roughly a 13-fold increase over the $1.8 million it spent in the non-election year 2011.

And ARL received almost all its revenues -- 97.6 percent -- from a single organization linked to billionaire conservatives Charles and David Koch, the Center to Protect Patient Rights, making it practically a wholly-owned subsidiary of the latter group. In that sense it's similar to another 501(c)4 nonprofit, American Future Fund, which obtained 92 percent of its 2012 funds from CPPR and one other Koch-linked group.

Under federal law, these nonprofits also don't have to disclose their donors, which is why they're often referred to as "dark money" groups. But ARL last year was at the center of a case brought by the state of California, which demanded to know, under state law, who donated the $11 million that ARL sent to the Small Business Action Committee, a group that was fighting a tax-hike initiative and supporting a measure to cut the influence of labor unions. Under order from a state judge ARL eventually revealed that it received the funds from CPPR; CPPR in turn got the money from Americans for Job Security, another dark money group.

California wound up fining ARL and CPPR a total of $1 million and requiring the Small Business Action Committee to disgorge the $11 million to the state.