The political network backed by billionaire industrialist Charles Koch doesn't plan to back Rep. Kevin Cramer, R-N.D., against Democratic Sen. Heidi Heitkamp in this fall's election.

Leaders of Americans for Prosperity made the announcement Monday, the final day of the Koch network donor conference in Colorado Springs, Colo.

The announcement comes as the organization has indicated it could support candidates outside the Republican Party. The group has been dissatisfied with some Trump administration initiatives, particularly its aggressive trade policy and tariffs.

Heitkamp, a centrist Democrat in a state President Donald Trump won by more than 30 percentage points in 2016. is considered one of the more vulnerable members of her party in the Senate. There are 10 Democratic senators up for re-election in states Trump won.

On Sunday, the one of the network's leaders said it would be open to backing Democrats who share the same policy goals. The group also unveiled a six-figure ad buy to target Trump's tariffs.

Tim Phillips, the president of AFP, told the group of donors that Cramer has been "inconsistent" and has not been an effective leader on "issues where the country needs leadership the most," which include removing Trump's trade barriers, as well as decreasing government spending.

Cramer responded to the group's announcement by leaving the door open to collaboration in the Senate, if he is elected.

"I respect the decision by the Koch network to not engage in the North Dakota Senate race. As I have always said, I work for the people of North Dakota and will always vote with them in mind. That is why I supported tax cuts, jobs creation, patient centered healthcare, strong borders, free, fair and reciprocal trade, and a strong military and veterans' care," Cramer said in a statement released by his campaign. "My voting record may not be exactly what every national organization wants, but it is exactly what the majority of North Dakotans expect. I look forward to working with the Koch organization on the things we agree on in the United State Senate.

The latest development comes after the group announced in June that it would be unleashing a digital advertising campaign thanking Heitkamp for co-sponsoring a bill that rolled back some banking regulations that came about after the 2008 financial crisis. The new measure passed Congress with bipartisan support.

The decision to withhold support from Cramer could potentially be a boost for Heitkamp as well as a massive blow to the Republican congressman, who is lagging behind his opponent in the fundraising game.

The most recent federal election commission records show Heitkamp raised $1.1 million between May 24 and June 30. Cramer, meanwhile, raised approximately $833,000. Heitkamp's campaign has just over $5.2 million; Cramer's has $2 million on hand.

"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," the Heitkamp campaign said in a statement.

The Koch network's decision to back away from Cramer is also a signal to the leaders of the Republican establishment that the group will not necessarily follow the guidance of GOP leadership.

Senate Republican leaders, including Majority Leader Mitch McConnell, R-Ky., had pushed Cramer to run against Heitkamp on the belief he was the best chance to flip the seat from blue to red. Since then, the ranks of Senate leaders have continued to publicly vouch for the North Dakota congressman.