"Social welfare nonprofits, also known as dark money groups because they don't have to report their donors, are allowed to spend money on politics as long as their primary purpose is social welfare. The groups often count so-called issue ads that stop short of advocating for or against a candidate and grants toward that social welfare mission. Since the Supreme Court's 2010 Citizens United decision allowed corporations and unions to spend directly on election ads, these nonprofits have turned into the vehicle of choice for anonymous spending, dumping more than $254 million into the 2012 elections.
Of the 150 or so social welfare nonprofits that reported spending to the Federal Election Commission during the 2012 election cycle, Crossroads was king, the biggest anonymous spender by far. Americans for Tax Reform came in fourth, with $15.8 million."
