Koch political arm not supporting North Dakota's GOP Senate candidate Kevin Cramer

Americans for Prosperity said it was due to his "inconsistency" on key issues.

Colorado Springs, Colo. --

Americans for Prosperity (AFP), the powerful political arm of the Koch political network, said Monday at a biannual conference of donors that it cannot currently support the Republican nominee for the U.S. Senate in North Dakota, GOP Rep. Kevin Cramer, because of his "inconsistency" on key issues important to the group such as trade and spending.

The North Dakota Senate race is one of ABC News' key "18 for '18" races this midterm cycle.

"We cannot support him at this time," AFP President Tim Phillips told a crowd of wealthy donors gathered at the network's bi-annual retreat in Colorado Springs, Colorado.

The groups said the move is an indication that it is "raising the bar" for Republican candidates to earn the support of the well-funded political apparatus.

"Bottom line, we need lawmakers to do more, so we need to expect more out of them. That’s why we’ve got a message for lawmakers across the country. We are raising the bar, raising expectations. That’s how this network will achieve more," said Emily Seidel, another top AFP official.

In June, AFP ran digital ads praising Cramer's opponent, Democratic Sen. Heidi Heitkamp, for her vote in support of reform to the Dodd-Frank financial regulation legislation.

Responding to the announcement from AFP, Heitkamp's campaign spokesperson Julia Krieger told ABC News, "When it comes leading on the pocketbook issues North Dakotans care about – from strong trade markets to responsible spending and cutting red tape for North Dakota businesses – Heidi has always been consistent: North Dakota comes first."

Phillips told donors "maybe [Cramer] needs to hear from you," adding that if the election were being held in 2014 or 2016, the group would "likely" have endorsed the Republican, who has held North Dakota's lone congressional seat since 2013.

Cramer has the endorsement of President Trump, and at a campaign rally in Fargo, North Dakota last month, said he will be with the president "100 percent of the time."

Seidel said that the Koch network looked at a situation where an elected Republican, "stood up in a Republican caucus meeting where they were debating a major piece of legislation and said flat out, ‘Don’t worry about the Kochs, they’re going to support Republicans regardless.’"

"We can’t keep falling into the trap of just doing what we need to do to get through November," Seidel said.

Officials for the Koch network said that AFP is currently involved in seven races this midterm cycle across six states: Wisconsin, Missouri, Tennessee, Michigan, Nevada and Florida.

The group has also launched an all-out effort to boost the nomination of Judge Brett Kavanaugh to the Supreme Court.

Phillips said activists with the group have placed over "500,000" calls in key states urging Senators to confirm Kavanaugh, focusing specifically on senators up for re-election in states President Trump won in 2016, including North Dakota, Indiana and Montana.