While the Koch brothers enjoy vast influence in the conservative movement thanks to their donor network and support for a variety of right-leaning nonprofits, the centerpiece of the Kochs’ political machine is Americans for Prosperity, the self-described “grassroots” organization best known for helping to fuel the rise of the Tea Party.

David Koch founded American for Prosperity (AFP) in 2004 after internal divisions caused another Koch-founded entity, Citizens for a Sound Economy, to dissolve into two separate groups (the other became FreedomWorks). Together with its companion “educational” foundation, AFP has become a leading force in anti-government activism and a major player in federal elections.

AFP’s activities include hosting the annual “Defending the American Dream Summit,” organizing nationwide campaigns on a range of issues (such as combating “climate alarmism” and opposing health care reform), and, increasingly, flooding the airwaves with attack ads targeting Democratic candidates. After spending nearly $40 million to influence the 2010 midterm elections, AFP spent a whopping $122 million in 2012. As of early February 2014, AFP had already spent close to $30 million against Democratic candidates in the 2014 midterms.

AFP boasts of having more than 90,000 individual donors, but a significant portion of its funding is tied to the Koch brothers. Although the group does not have to disclose its donors, two organizations associated with the Kochs, Freedom Partners and the Center to Protect Patient Rights, have reported contributions totaling more than $48 million since 2009.