The identities of the donors behind most of the billions of dollars that fund U.S. political campaigns are publicly disclosed. Candidates, parties and political action committees — including the super PACs that are allowed to accept unlimited amounts of money — regularly provide the Federal Election Commission with the names of all donors who give more than $200. But a growing share of the funds that grease the wheels of U.S. electoral politics is dark money, the donors of which keep their identities secret.

The two most common vehicles for dark money are politically active nonprofits and corporate entities, such as limited liability companies. Certain politically active nonprofits — notably those formed under sections 501(c)(4) and 501(c)(6) of the tax code — are generally not required to publicly disclose their donors. And limited liability companies formed in states such as Delaware and Wyoming are essentially black boxes through which donors can make secret donations to super PACs or to intervene directly in election campaigns.

During the 2012 election cycle — the last time the presidency was at stake — dark money groups pumped about $300 million into advertising for or against candidates, according to the nonpartisan Center for Responsive Politics. These groups also spent hundreds of millions of dollars on political ads focused more on issues than on candidates. The most notable example? Americans for Prosperity, the flagship nonprofit of the conservative billionaire brothers Charles Koch and David Koch.

Read More- Al Jazeera America