Colorado Springs, Colorado (CNN) The influential Koch political network announced Monday it is not supporting Republican Rep. Kevin Cramer in his race to unseat vulnerable Democratic Sen. Heidi Heitkamp in North Dakota -- the latest sign the conservative group is frustrated with the current state of the GOP.

The decision for now to stay out of a pivotal 2018 Senate race will likely send shockwaves through the Republican Party and fits with a broader theme from the Koch network's summer meeting that the network feels like it has been "taken for granted" by the GOP.

Top officials at Americans For Prosperity, the political and policy arm of the Koch network, said the group is not currently supporting Cramer because he is not leading on central policy priorities for the Koch network.

"If this were 2016, we likely would have gone ahead and endorsed" Cramer, said AFP President Tim Phillips. "But we're raising the bar."

Speaking to the network's backers Monday, the final day of their summer meeting in Colorado Springs, Phillips criticized Cramer for his support of a $1.3 trillion spending measure earlier this year and his reluctance to take on the White House on trade and tariffs.

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