Sen. Pat Roberts is locked in a tight re-election battle against independent Greg Orman.

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The U.S. Chamber of Commerce is endorsing Kansas Sen. Pat Roberts

Roberts is trailing independent candidate Greg Orman in the key race

Topeka, Kansas CNN  — 

Embattled Republican Sen. Pat Roberts added to his cavalry of endorsements Monday, receiving the backing of the U.S. Chamber of Commerce.

Roberts, a conservative three-term senator, is in an unusually tough race in deep-red Kansas with independent businessman Greg Orman, whom Roberts attacked hard about what he’s calling questionable business dealings with Rajat Gupta, a former Wall Street executive convicted of insider trading.

“He isn’t honest about his liberal ideology, and he isn’t coming clear about his business record,” Roberts said. “Mr. Orman is using his business record as a sole qualification for his candidacy, but the truth is Mr. Orman built his business career working with one of Wall Street’s biggest criminals, avoiding taxes, and laying off hard-working Americans.”

Roberts’ low poll numbers have garnered national attention in a year Republicans could win a Senate majority. It’s been over 80 years since Kansas elected a non-Republican senator, and party members don’t want the Sunflower state to be the reason they remain in the minority during the next Congress.

The Chamber of Commerce endorsement is critical for Republicans who represent themselves as business allies. The organization typically shows support for Republican candidates, which could include ads and other financial support.

“We’re all in for Senator Roberts. Period,” Rob Engstrom, a senior vice president of the U.S. Chamber of Commerce, told CNN. “We’re going to clearly point out where Mr. Orman and his liberal record with his liberal allies stands on the issues. And once Kansas voters hear that and believe that and know that, Senator Roberts will win.”

Republican Party members from all spectrums concerned about winning a majority have also come to Kansas to campaign with the senator.

Bob Dole, a former GOP presidential candidate, Senate majority leader, and member of the Kansas congressional delegation, campaigned for Roberts last month, as did other establishment party members including former former Florida Gov. Jeb Bush and Sen. John McCain of Arizona. Former presidential candidate Mitt Romney will be in Kansas later this month, Roberts said.

Tea party supporters also have given Roberts the support he’ll need to win in November, even after their preferred candidate, Dr. Milton Wolf, lost to him in the primary earlier this year. Sarah Palin has already stumped for Roberts, and Sen. Ted Cruz of Texas will kick off a statewide bus tour campaign this Friday.

Asked why Orman’s business experience and position in favor of immigration reform like the Chamber’s didn’t qualify him for the endorsement, Engstorm said, “I would argue there are very few positions where we share a common view. Dodd-Frank, American energy exploration, cap-and-trade, Obamacare. He’s either on the wrong side or won’t say where he stands.”

Engstrom didn’t mince words to show his support for Roberts’ business record. “This is the senator – this is the man – who is pushing back against Obama and Harry Reid, and Mr. Orman is not. He’s absent,” he said.

Orman didn’t return the candidate questionnaire used to decide endorsements within the organization that represents over 300,000 members, Engstrom noted.

Roberts isn’t the only Republican having trouble in the polls this year in Kansas. Gov. Sam Brownback’s re-election is also in question.

Asked by CNN whether Brownback is dragging down his campaign, Roberts replied, “I will let Governor Brownback speak for himself, but I think – I think he’s coming back.”