David Koch (pictured) and his brother Charles reportedly supported Wisconsin Gov. Scott Walker for president. Reuters

Scott Walker’s departure from the 2016 presidential race represents not just the end of the Wisconsin governor’s campaign, but a stunning blow to two of the GOP establishment’s most powerful would-be kingmakers: Charles and David Koch. As Walker championed the Kochs’ archconservative anti-union agenda in Wisconsin, the two industrialists and their political network delivered more than $11 million to his campaigns and to groups supporting him in Wisconsin.

As recently as April, David Koch attended a Republican fundraising event with Walker and told donors there he and his brother believed the governor would be the party’s nominee.

“When the primaries are over and Scott Walker gets the nomination,” Koch told the donors, according to the New York Times. The newspaper reported attendees at the event said Koch went even further, saying Walker should be the nominee.

Yet with outsider candidates in both parties riding a wave of anti-establishment fervor, even the imprimatur of Koch Brothers support failed to stem Walker’s swift decline. Since reaching 18 percent in the Republican primary polls in Iowa, Walker has faded -- most recently failing to register any support in a CNN poll.

With Walker out of the race, it remains unclear which candidate may benefit from the Koch Brothers vast fundraising network, which has pledged to spend nearly $900 million on the 2016 presidential campaign. While the Kochs excluded Kentucky Sen. Rand Paul and New Jersey Gov. Chris Christie from their most recent conference -- hosted by their affiliated organization, Freedom Partners -- they did invite former Florida Gov. Jeb Bush, Texas Sen. Ted Cruz, Florida Sen. Marco Rubio and former Hewlett-Packard CEO Carly Fiorina to the event. At the conference, the candidates met privately with donors and held their own question-and-answer sessions on stage, Politico reported

Some of those latter candidates have longstanding relationships with the Kochs. In 2010, for instance, their company’s political action committee held a fundraiser for then-senate candidate Fiorina. In 2005, Koch Industries stood to benefit from a decision by Jeb Bush’s administration to intervene in an environmental dispute and allow the company’s affiliate to build a controversial pipeline in Florida. Meanwhile, a poll of GOP donors at a recent Koch-organized conference found strong support for Rubio.