Rep. Kevin Cramer (R-N.D.) at a 2016 event in Bismarck. He is challenging Sen. Heidi Heitkamp (D-N.D.). (Charles Rex Arbogast/AP)

The Koch political network announced Monday that it does not currently plan to support Republican Kevin Cramer in his effort to unseat Sen. Heidi Heitkamp of North Dakota, one of the most vulnerable Democrats up for reelection this November.

Heitkamp’s race is a top pickup opportunity for Republicans, who are trying to retain their slim two-seat majority in the Senate. Heitkamp, the only Democrat who holds statewide office in North Dakota, is running for reelection in a state that Donald Trump won by more than 35 points.

The Koch network’s decision places it at odds with President Trump, who campaigned for Cramer at a rally in Fargo last month.

The network, which is backed by billionaire industrialist Charles Koch and like-minded donors, also has no current plans to support Senate candidates in Nevada and Indiana, two key red-state races that are pickup opportunities for Republicans this fall, according to details it released Monday.

In all, Koch groups are backing GOP candidates in just four Senate races right now and steering clear of five out of the eight toss-up races.

The decision by the conservative political network to withhold its firepower in pivotal states — at least for now — comes as top Koch officials are expressing frustration with Trump and Republican Party leaders over trade policies and the rhetoric in Washington.

As Koch officials laid out their plans for the 2018 midterms for more than 500 donors gathered at a luxury resort here, they warned that the GOP should not take its resources for granted.

Tim Phillips, president of Americans for Prosperity, the network’s main political arm, said the group is more carefully assessing which candidates it will back, based on their support of the network’s free-market policy priorities.

“We’re raising the bar,” he said. “We’re raising expectations because we’ve got to change the trajectory of this country.”

AFP chief executive Emily Seidel sought to underscore the importance of the network’s independence, saying a GOP senator who she did not name reportedly told colleagues at a Republican caucus meeting: “Don’t worry about the Kochs. They’re going to support Republicans regardless.”

“And by Kochs, he was talking about all of you,” she told donors. “We can’t keep falling into the trap just doing what we need to do to get through November.”

Phillips said that “if this were 2016 or 2014, we would likely have just gone ahead and endorsed” Cramer. But he said the three-term congressman has been “inconsistent” on a range of issues, including the Affordable Care Act, free trade and immigration policies. He also noted Cramer’s support for agriculture subsidies.

“If Cramer doesn’t step up to lead, that makes it harder to support him,” Phillips said.

Earlier this year, AFP ran a digital ad thanking Heitkamp for co-sponsoring a bill that rolls back regulations placed on banks after the 2008 financial crisis.

Cramer did not immediately respond to a request for comment.

The GOP congressman still has other big-money backers on his side. Restoration PAC, a conservative super PAC largely funded by Richard Uihlein, a wealthy shipping-supplies magnate from Illinois, said Monday that it planned to continue to support him.

And Dan Eberhart, an oil-industry executive who attended the Koch summit and is a top fundraiser for Cramer, said he is sticking by him.

“I think the Koch network is tremendous in what they accomplish philanthropically and politically in general,” he said. “They are wrong on Cramer.”

Cramer, Eberhart said, “is committed to President Trump’s agenda, which I think is what many conservative voters feel in their biggest motivations.”

In an interview with reporters Sunday, Charles Koch expressed regret for supporting some of the Republican lawmakers his network has backed in the past, although he declined to single any out by name.

“We’re going to be much stricter” in endorsements this year, he said.

AFP is still expected to be a powerful force for conservative candidates and causes this midterm cycle. Officials have reiterated their plan to spend up to $400 million in the cycle on public policy issues and political campaigns.

The network will get involved in dozens of races this fall, with plans to back GOP Senate candidates in Wisconsin, Missouri, Florida and Tennessee and gubernatorial candidates in Michigan and Nevada, officials said Monday.

Among the Republicans who will get robust support from Koch groups is Rep. Marsha Blackburn, who is running for U.S. Senate in Tennessee.

And in a private presentation to donors, AFP officials touted the stances of GOP Senate challengers Rick Scott of Florida, Josh Hawley of Missouri, Matt Rosendale of Montana, Patrick Morrisey of West Virginia, and Leah Vukmir and Kevin Nicholson of Wisconsin.

Meanwhile, the network is plowing resources into supporting the confirmation of Trump’s second pick for the Supreme Court, federal judge Brett M. Kavanaugh, including in states where Democrats are the most vulnerable this fall. AFP has mobilized its nationwide network of activists, focusing on senators in Alabama, Alaska, Florida, Indiana, Montana, North Dakota, Ohio and West Virginia.

Sean Sullivan contributed to this report.