Charles Koch first likened candidate Donald Trump’s plan to ban Muslim immigrants to something Adolf Hitler would have done in Nazi Germany.

The billionaire industrialist and his chief lieutenants offered a more delicate response this weekend when asked about President Trump’s plan to block immigration from seven Muslim-majority countries. They described Trump’s plan as “the wrong approach” that violated Koch’s dedication to “free and open societies.”

The criticism comes as the Koch network, among the most powerful conservative groups in the nation, works to strike a delicate balance in the early days of the new administration. The Kochs refused to support Trump’s candidacy last fall, but they now see a once-in-a-lifetime opportunity to influence the White House and the Republican-controlled Congress.

Their optimism is fueled by strong relationships inside the administration, despite their vow to oppose Trump’s policies if they deviate from the Koch brothers’ conservative priorities.

Trump critics were easy to find at the California desert resort this weekend, where attendance at a semi-annual conference was limited to the 550 people who donate at least $100,000 each year to the various conservative political and policy groups backed by Charles and David Koch.

The critics included Charles Koch himself, although the conservative patriarch did not mention Trump by name Sunday as he warned that the nation is facing a moment of “tremendous danger.” He said the nation could “go the authoritarian route … or we can move toward a free and open society. So this is our opportunity.”

Still, the Koch network says it’s confident about its ability to shape the direction of the Trump administration’s policies from the inside.

“Many former network staffers that are in the White House now remain good friends of ours. So we’re in constant contact with them,” said Koch spokesman James Davis. “Conversations have been open and continue to be.”

There is perhaps no bigger Koch ally than Vice President Mike Pence, whose staff and ideology has been in close alignment with the Kochs for years.

Charles Koch spoke directly with the vice president on the phone days before his inauguration as Pence considered hiring a Koch communications staffer, Stephen Ford, to serve as his chief speechwriter. Ford was soon hired, along with former Koch chief Marc Short, who now serves as the White House legislative director.

“The reason we’re optimistic … is really Mike Pence,” said Doug Deason, a prominent Trump supporter and major Koch donor. “If you think Cheney had power in Bush White House, just watch and see what happens with Mike Pence.”

Several reporters, including one from The Associated Press, were invited to attend the weekend conference. As a condition of attending, photographers were not allowed and reporters were not permitted to identify any donors without their permission.

Koch and his powerful allies insist they will challenge Trump when his policies don’t align with their conservative vision.

The network plans to spend between $300 million and $400 million over the next two years to shape policy and politics, much of it devoted to its nationwide grassroots network. While there has been much talk of Trump allies creating an outside group to help promote his agenda, the Koch network’s capacity to communicate directly with voters on the ground in key states has no political rival.

The Koch’s “secret sauce” is “the accountability play,” said Mark Holden, who serves as senior vice president, general counsel and corporate secretary of Koch Industries,

“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. But if we can we will support them, regardless of who’s in office,” he said.

Like Trump, the Kochs favor efforts to cut government regulation and replace the federal health-care system. They do not share the president’s plans for a massive infrastructure spending or his crackdown on immigrants from Muslim-majority countries.

“The travel ban is the wrong approach and will likely be counterproductive,” network co-chair Brian Hooks said Sunday.

“Our country has benefited tremendously from a history of welcoming people from all cultures and backgrounds,” he said. “This is a hallmark of free and open societies.”

The Koch network’s many donors also lashed out at Trump’s immigration order.

“It doesn’t do any good for us to be positioned as hating whole classes of people,” said Erick Brimen, a Venezuelan native who became a U.S. citizen last year and now manages a private equity firm.

“What has made America great always is that this has been a place that has welcomed the best and the brightest,” said Brimen. “The message needs to be very loud and clear that we continue to be such a place no matter where you come from.”

There are also deep concerns about a new president with no long-term commitment to conservative priorities like free trade, free markets and small government.

“Our suspicion is we’re going to get three parts good and one part bad,” said Chris Wright, a Colorado-based energy entrepreneur. “We’re worried about the one part bad.”

Without naming Trump, Hooks noted that Republicans opposed President Barack Obama’s stimulus and would should do the same if the new president follows through on his pledge to support a massive infrastructure package. Others promised to fight what they called “crony capitalism” in the new administration, reminding conservatives they fought Obama’s support for private companies like Solyndra and should do the same when Trump picks winners and losers in private business.

Hooks and others also repeatedly raised pointed objections to Republican plans to adopt a “border adjustment” tax or new tariffs.

“We’re going to have the courage to oppose bad policies…regardless of who proposes them,” Hooks declared.