Billionaire Charles Koch said Sunday he worries President Donald Trump’s actions on trade and tariffs put the booming U.S. economy at risk of recession.

“It depends on the degree” of the trade conflict that the U.S. pursues with countries such as China and Canada, Koch said in Colorado during a rare on-the-record meeting with reporters. “If it’s severe enough it could” end in recession.

“Any protectionism at any level, and certainly at the national level, is very detrimental,” Koch said. “Every nation that’s prospered is one that didn’t engage in trade wars.”

It would be “disastrous,” Koch said, if the U.S. were to “completely close” itself off from trading with other nations. The Trump administration hasn’t proposed that step. But Trump said this month, for example, that he was ready to put tariffs on all goods imported from China. “I’m ready to go to 500,” Trump said on CNBC on July 19, referring to $500 billion.

National Security

Trump has already imposed tariffs on steel and aluminum imports in the name of national security, as well as duties on certain Chinese products in response to allegations of intellectual property theft. That’s drawn retaliatory tariffs on soybeans and other U.S. goods in an escalating conflict, although Trump struck a truce with the European Union last week pending further negotiations.

The U.S. economy in the second quarter expanded at its strongest pace since 2014, the government reported on Friday. But many economists see growth tailing off from here, and the potential for a trade war are part of their assessments.

Charles and brother David Koch didn’t support Trump in the 2016 campaign, but the conservative political and policy donor network they built has since praised his administration’s efforts to cut taxes and regulations. A White House spokesman didn’t immediately respond to an email seeking comment.

Koch’s comments came as donors to the network are gathered for a three-day meeting at a luxury resort in Colorado Springs.

The network, with more than 700 donors who give at least $100,000 per year, has convened such gatherings twice annually since 2003. It has long opposed protectionism and promoted the benefits of free trade, as have other most other groups aligned with Republicans.

Battleground States

So far this weekend, the network sought to downplay its role in this year’s midterm congressional campaign, even as ads it paid for have hammered Democrats in battleground states. Planned spending on campaign-associated activities was prominent when the network last assembled in January.

Since then, analysts and polling have increasingly suggested Democrats have a good chance of winning control of the U.S. House in November’s midterm elections, in line with historical trends. The party needs a net gain of 23 seats to do that.

In June, the Koch network said it was planning a “multi-year, multi-million-dollar” campaign to promote free trade and oppose Trump’s moves to impose tariffs. The effort is to include advertising, voter mobilization and lobbying.

Some of the elected officials attending the gathering include Governor Rick Scott of Florida, who’s running for U.S. Senate; Kentucky Governor Matt Bevin; Senator John Cornyn of Texas; Senator Tim Scott of South Carolina; Representative Marsha Blackburn of Tennessee, who’s running for U.S. Senate; Representative Doug Collins of Georgia; and Nevada Attorney General Adam Laxalt, who’s running for governor. All are Republicans.

Plans call for the network to spend about $400 million on state and federal policy and politics during the two-year cycle that culminates with November’s balloting, a 60 percent increase over 2015-16. Besides trying to influence electoral politics, the network also works on education, criminal justice, workforce and poverty issues.