President Donald Trump lashed out at the powerful political network started by billionaires Charles and David Koch after it broke with a 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. I never sought their support because I don’t need their money or bad ideas,” Trump tweeted on Tuesday morning.

Trump alleged that his policies have “made them richer” but 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.”

The network’s decision 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.

“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.

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

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