Charles and David Koch are probably, justifiably, the richest conservative bogeymen in the U.S. Collectively, they're referred to as the Koch brothers—though that excludes their less notorious brothers Frederick and Bill. Charles and David are worth an estimated $50 billion each, thanks to Koch Industries, the sprawling business empire that covers petroleum, chemical manufacturing, timber, ranching, finance, the list goes on. They're hardcore libertarians and influential behind-the-scenes political activists, providing money for so many right-wing think tanks, political organizations, and PR campaigns that investigative reporter Jane Mayer wrote a 500-page book, Dark Money, about their shockingly successful efforts to reshape American politics. Their funding helped to drive the faux-grassroots Tea Party movement and established the libertarian Cato Institute, the think tank that crusades against progressive causes like health-care reform and environmental regulation. And now, the Kochs are turning their attention to the Democratic Party.

In a memo obtained by CNBC, Emily Seidel, CEO of the Koch-affiliated political-action committee Americans for Prosperity, announced that the organization would be backing incumbent Democrats against progressive primary challenges in the upcoming congressional primaries. The memo laid out AFP's new objectives, including:

Support the primary election of lawmakers, regardless of political party, who stick their necks out to lead diverse policy coalitions. The threat of being primaried prevents policymakers from leading on difficult issues and driving principled policy reforms. AFP or AFP Action will be ready to engage contested U.S. Senate, U.S. House, and state-level primary races, including Republican, Democrat, Independent or otherwise, to support sitting legislators who lead by uniting with others to pass principled policy and get good things done.

Those "good things" include, for example, the Republican tax cuts from 2017, which slashed the taxes for Koch Industries by as much as $1.4 billion a year. Considering that the Kochs contributed $20 million to getting the bill passed, the return on investment is pretty good.

The twisted part of the claim that primaries keep politicians from "leading on difficult issues" is that the Koch network, as Mayer documented in her book, regularly funded primary challenges against incumbent Republicans who didn't stick closely enough to Koch-endorsed policies. And since they're known for cynically calculating decisions, it should raise all sorts of alarms that they now want to get involved in Democratic primaries. By bankrolling incumbents, they can potentially shut out future progressive upstarts like Alexandria Ocasio-Cortez and Ayanna Pressley, both of whom beat long-sitting congressmen in 2018. The most ominous part of this plan is how much it dovetails with the objectives of the Democratic establishment, like the Democratic Congressional Campaign Committee, ostensibly dedicated to electing Democrats to the House of Representatives. The DCCC, which is consistently to the right of the party's voters, recently announced that it would blacklist any consultants or vendors that worked with candidates running against Democratic incumbents.

The Kochs and other libertarian billionaires have probably realized by now that centrist Democrats—self-described liberals who support tax cuts, deregulating industries, and privatizing public services—are more reliable allies than ambitious and popular progressives with a concrete political agenda. Ocasio-Cortez, for example, has only been in office for six months but has helped make Medicare for All and the Green New Deal—which would be a particular headache for Koch Industries—national issues during a presidential primary. The Joe Bidens of the party are much more sympathetic to the plight of the super-rich than the Elizabeth Warrens, after all. And since today's Republicans can't go farther right than they already have, it makes good business sense to now start pulling Democrats in that direction.