Which one of these is not like the others? A) Democratic Party, B) Republican Party, C) the Koch Brothers.

The correct answer is C. (Partial credit if you answered A, given that the GOP has become the party of Koch. More on that here). Here’s the answer key: where the Democratic and Republican parties are centuries-old political institutions governed by campaign finance regulations, the Koch brothers are self-interested billionaires committed to pouring unlimited amounts of cash into influencing this fall’s mid-term elections.

Yet according to the Washington Post, the Koch brothers’ political arm, Americans for Prosperity, is effectively the third-largest political party in the country. “This year, the [Koch brothers’] network is likely to outstrip other organizations on both the left and the right with spending on television ads and on-the-ground organizing,” writes the Post’s Matea Gold, who notes that AFP and the Koch network are poised to spend upwards of $300 million on this fall’s elections. For decades, the Kochs’ political agenda has included unlimited political spending, and it’s not hard to understand why, when the post-Citizens United era has allowed these billionaires to amass a political network akin to our country’s longstanding political parties.