President Donald Trump lashed out at the powerful public policy and political network built by billionaires Charles and David Koch after it criticized his leadership and broke with its tradition of backing Republican candidates by declining to support the party’s pick against a vulnerable Democratic senator in North Dakota.

“The globalist Koch Brothers, who have become a total joke in real Republican circles, are against Strong Borders and Powerful Trade,” Trump tweeted Tuesday. “I never sought their support because I don’t need their money or bad ideas.”

Trump alleged that his policies have “made them richer” and that they “want to protect their companies outside the U.S. from being taxed,” while he supports the American worker. In another tweet Trump called them: “Two nice guys with bad ideas.”

James Davis, a spokesman for the network, didn’t immediately respond to an email seeking comment.

The brothers didn’t support Trump in the 2016 campaign, but their network has since praised his administration’s efforts to cut taxes and regulations. More recently, it has criticized his actions on trade issues.

Keeping the network happy is important to Republicans, especially in election years. It plans 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 organization also works on education, criminal justice, workforce and poverty issues.

The network’s decision Monday not to support Representative Kevin Cramer against Democratic Senator Heidi Heitkamp in North Dakota was cast as a warning to other Republicans who might be tempted to stray from the free-market, fiscally restrained approach backed by the Kochs and their followers.

The decision not to back Cramer, as the network sought to put on a more bipartisan face, was announced at a briefing for more than 500 donors gathered for a three-day meeting at a luxury resort in Colorado Springs, Colorado.

“We can’t support him at this time,” said Tim Phillips, president of Americans for Prosperity, the network’s flagship political organization.

Heitkamp is one of 10 Senate Democrats who face re-election in November in states Trump won in 2016. While polls and analysts suggest Democrats have a strong chance of winning the 23 seats they need to gain control of the House, their odds of winning a Senate majority are much slimmer.

Trump’s tweets are aligned with comments former White House chief strategist Steve Bannon made a day earlier. “We don’t have time to have some theoretical discussion and to have their spokesman come out and say the president is divisive,” he told Politico.

Charles Koch, 82, chairman and chief executive officer of Koch Industries, told reporters Sunday he worries Trump’s actions on trade and tariffs put the booming U.S. economy at risk of recession.

While senior officials from the network had blamed Trump for the nation’s divisions a day earlier, Koch stopped short of that.

“We’ve had divisiveness long before Trump became president,” he said in rare on-the-record exchange with reporters. “I’m into hating the sin, not the sinner.”