Koch called the choice between Trump and Hillary Clinton like opting for cancer or a heart attack. And Trump bashed big-money donors, deriding his Republican rivals as "puppets" who begged at Koch's door.
Not surprisingly, Koch and his allies largely sat out the presidential election, and Trump won without them. Normally such a high-profile snub would carry a steep political price.
But Koch's network of conservative advocacy groups has exerted surprising sway in the Trump administration, scoring some early victories and pushing its priorities to the top of the White House agenda.
Its influence is likely to grow after the ouster of Trump's top strategist, Stephen K. Bannon, amid the White House turmoil over neo-Nazi violence in Charlottesville, Va. Bannon had clashed with several of Trump's top aides, including those aligned with the Koch crowd, over his hard-right views.
Bannon's populist agenda, with its nationalist, nativist and anti-immigration bent, found few fans among the business-oriented, small-government conservatives aligned with Koch.
With Bannon back at Breitbart News, a far-right website, the question is whether he will still have Trump's ear from the outside while Koch and his cohorts retain strong allies in the White House.
Trump said nothing about Bannon's exit on Friday, but on Saturday he thanked his former aide on Twitter for taking over his campaign last summer. The message did not refer to his work in the White House.
"I want to thank Steve Bannon for his service," Trump tweeted. "He came to the campaign during my run against Crooked Hillary Clinton - it was great! Thanks S."
Hours later, Trump wished Bannon well at Breitbart, "maybe even better than before" in the fight against what Trump called "Fake News."
Over the last seven months, the Koch group's work has quietly shaped some of the White House's policy victories.
It started with the quick rollback of a dozen Obama-era environmental and labor regulations, a to-do list compiled by Koch-backed groups even before Trump took office.
Soon after, the Koch-backed Concerned Veterans for America was instrumental in passage of legislation to make it easier to fire employees at the beleaguered Veterans Affairs Department. The end-run around civil service protections offered a blueprint that could be replicated in other federal departments.
In July, the Koch network celebrated the official demise of the proposed border-adjustment tax. House Speaker Paul D. Ryan (R-Wis.) had backed the idea, but it was bitterly opposed by many business groups, including Koch and his allies.
After months of intense campaigning by the Koch network — 10,000 phone calls to lawmakers' offices and $2 million on tax-reform ads and other advocacy — GOP congressional leaders and the White House announced that the upcoming tax-reform package would not include a border-adjustment tax.
The Koch network's efforts to influence the Trump team were aided when the White House hired several Koch-affiliated alumni as key aides for a president who arrived without any government experience or a deeply staffed bench.
"The vacuum in Trump not having his own network is filled by people who've been cultivated for years by the Koch network," said Richard L. Hasen, a professor at the UC Irvine law school and an expert in campaign finance.
Also helpful is a Republican-led Congress, where many members depend on the network's political and financial backing for reelection and fear attacks if they stray from the libertarian, small-government orthodoxy.
Even without being active in the presidential race, the network spent $750 million during the 2016 election cycle, including $250 million on campaign ads, voter engagement and other efforts to advocate for issues and shape public opinion.
Through its think tanks, conservative groups and political operations, the network brings organizations together around Koch's libertarian-leaning small-government pursuits. It is funded by donations from more than 700 members who each pay $100,000 annual dues to attend its summits.
At a summit in June, when the 81-year-old Koch welcomed hundreds of wealthy donors to the network's annual seminar in Colorado Springs, Colo., he marveled at how far they had come in the decade-plus since its founding.
"When I look at where we are, at the size and effectiveness of this network, I'm blown away," Koch said as guests and lawmakers mingled at the posh Broadmoor resort. "We are more optimistic now about what we can accomplish than we've ever been."
The Koch network plans to spend nearly $400 million for campaign ads and other efforts to shape public opinion before next year's midterm election.
To be sure, the failure of Congress to pass healthcare legislation this year stands as a glaring setback for the Koch network. It emerged on the national political stage during the unsuccessful GOP fight to block passage of the Affordable Care Act, also known as Obamacare, in 2010.
After having spent millions to help Republicans win the House majority in 2010 and the Senate in 2014, some members of the network say they are so frustrated they say they will withhold campaign cash for the 2018 midterm until GOP lawmakers deliver.
Ironically, passage of tax reform is also now in jeopardy with the continued White House upheaval and staff shake-ups.
But 200 days into the new administration, Charles Koch and his brother, David — who are tied at No. 8 on the Forbes list of the world's wealthiest individuals — appear as influential as ever.
On Saturday, Vice President Mike Pence, a longtime ally, was scheduled to deliver the keynote address at the network's annual activist summit in Richmond, Va. Commerce Secretary Wilbur Ross replaced Pence in a schedule change after the violence in Charlottesville, Va.
Earlier this month, Treasury Secretary Steven T. Mnuchin was featured at a Koch-backed event in Washington with Marc Short, the White House legislative director, about the administration's tax plan. Short is a former aide to Pence and onetime president of Freedom Partners, a Koch-aligned group.
Democrats have been furious, reviving the specter of what they call the "Kochtopus," with its alleged reach into almost every federal government policy and wealthy donors secretly keeping lawmakers in line.
Senate Minority Leader Charles E. Schumer (D-N.Y.) recently warned congressional Republicans not to cater to wealthy donors' priorities during the tax debate this fall.
"Don't give breaks to the top 1% — everyone knows they don't need it," Schumer said on the Senate floor. "Have the courage to break free from the Koch brothers and the special interests."
Koch supporters relish such criticism. "We enjoy getting attacked by the angry left," said Texas donor Doug Deason, who attended the June gathering in Colorado. "It means we're getting something accomplished."