Charles and David Koch, the billionaire libertarian-ish brothers and longtime Republican Party patrons, never did like Donald Trump. During the 2016 election, they refused to contribute to Trump’s candidacy, noting that they would instead spend their $300 million to prop up Republican candidates in local races. They remained aloof throughout 2017, with Charles suggesting that Trump’s Muslim ban was reminiscent of Nazi-era racism, and both brothers implying that they would wait it out before backing Trump, who had begun to rail about tariffs. “We’re principled, and if we can’t get comfortable with the policies that are in place, then we’re not going to support them,” said Mark Holden, Koch Industries’s top lawyer. Though they made several attempts to influence the White House’s policy through their connections with top figures like Mike Pence, the president’s recent gesture toward a trade war with China represented a proverbial final straw. “From the beginning we've said that tariffs and protectionism is a bad idea,” Tim Phillips, president of Americans for Prosperity, the Kochs’ political organization, told CNBC. “[The White House has] explained their reasoning behind it and we just strongly disagree.”

Even then, the Kochs still hoped to push their agenda through Congress, donating hundreds of thousands of dollars to individual representatives and Republican fund-raising groups, and announcing that they would spend up to $400 million to defend their control. But on Sunday, during an annual seminar with roughly 500 top conservative donors, Americans for Prosperity announced it would no longer solely support Republican candidates, formalizing a visible schism within the G.O.P.’s donor class. As Charles Koch put it to reporters, “I don’t care what initials are in front or after somebody’s name.” His comments seemed like a foregone conclusion following several Kochworld attacks on the Trump administration’s policies over the weekend, with the brothers and their spokespeople flaming the White House left and right. “It’s a bail-out to bad policy,” Koch network spokesperson James Davis told reporters of the administration’s announcement that it would spend $12 billion to relieve farmers impacted by its trade war. “You can’t make this up. We put tariffs supposedly to put pressure on China and then it actually hurts farmers here. Crops waste away in the field. Then you pull a Depression-era program out to bail out farmers and make them whole. But who’s underwriting our debt?” Another Koch official lamented that the “divisiveness of this White House is causing long-term damage.” Koch himself called Trump’s tariffs “unfair to the people.”

“I know this is uncomfortable,” said Emily Seidel, the C.E.O. of Americans for Prosperity, during a speech. “If you are a Democrat and stand up to [Senator] Elizabeth Warren ”—the regulatory-allergic Kochs’ ultimate progressive boogeyman—“to corral enough votes for financial reform that breaks barriers for community banks and families, you’re darn right we will work with you. . . . If you are a Republican who sits on the committee that wrote the worst spending bill in our country’s history and you voted for it, you’re darn right we will hold you accountable.”

The Kochs’s hostility toward Trump isn’t new, though their rhetoric seems to mark a turning point. A.F.P. has been subtly instigating this agenda for months, running a not insignificant volume of ads blasting Republicans for voting in favor of Trump’s controversial trillion-dollar spending package, and going out of their way to advertise in support of Democrats who embrace their agenda, such as North Dakota Senator Heidi Heitkamp, who voted to roll back Dodd-Frank regulations on community banks. (Heitkamp, incidentally, faces a tough race in a vulnerable seat this year.) Perhaps the brothers Koch hoped that overtly voicing their objections would lure some Republicans back into the free-market fold, thereby preserving their Congressional majorities.

Whatever their motivation, Trump loyalists were not pleased. “It’s wrong, it’s stupid and it shows contempt for the hardworking grassroots folks that delivered the victory that got your tax cut,” Steve Bannon, former chairman of the ardently pro-Trump Web site Breitbart News, immediately told Politico. “Charles Koch is a good man, but 100 days before an election that will determine the direction of the country is not the time to tell us that you are prepared to work with Democrats that support parts of your progressive agenda,” he added. “What they have to do is shut up and get with the program . . . And here’s the program: ground game to support Trump’s presidency and program, [and] victory on November 6.”

It’s possible that Bannon, who is in the midst of his own populist comeback campaign in Europe, is overreacting. After all, the Koch camp is still spending massive amounts to keep Republicans in power post-2018 midterms—if the G.O.P. retains control of Congress, it will by default be pushing a Trumpian agenda. It could be that the Kochs’ willingness to speak out against the White House’s trade policy, then, is more to assuage their consciences than to damage the president. But it certainly sets them apart from Trump’s rabid isolationist base, lending credence to Republican fears that Trump’s trade war, which is already dinging American businesses and costing American consumers, may come home to roost among Republican voters.