MINOT, N.D.-The 2018 election cycle was always going to be a high wire act for incumbent Sen. Heidi Heitkamp. An exercise in peeling off enough Republican voters from her Republican opponent to win without hemorrhaging so many voters from her liberal base that she loses.

For added difficulty, Heitkamp must pull this off while campaigning with an actual voting record for the first time in her political career.

Remember that the senator's previous experience in elected office was all in the executive branch.

Unfortunately for Heitkamp and her supporters, the wire grows narrower.

The incumbent has been running to the right. Earlier this month she launched a radio ad bragging about her votes in lockstep with President Donald Trump. This week Heitkamp launched a television ad touting compliments Republican senators have paid her.

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It's too early to tell if these ads are having any impact on Heitkamp's plummeting approval numbers-according to the Morning Consult poll the incumbent's 60 percent approval rating in July of last year had fallen to just 44 percent earlier this year-but they can't be helping the erosion of support in her liberal base.

"We rallied so hard for her, but when her hand was forced she basically sold out to big oil," Marlo Hunte-Beaubrun told The Associated Press this week.

Hunte-Beaubrun is a member of the Standing Rock Sioux Tribe who helped organize the Native American vote for Heitkamp during her 2012 campaign. She was also a statewide candidate for the North Dakota Democratic Party in the 2016 cycle, running for the Public Service Commission.

Hunte-Beaubrun described Heitkamp's treatment of Native American voters as a "kick in the stomach."

She's referring to Heitkamp's perceived support of the Dakota Access Pipeline, and although that support wasn't nearly fulsome enough for many proponents of that project, it was clearly a bridge too far among the anti-pipeline activists in the senator's base.

"The majority of the people here feel the same way I do - she chose oil over Indians," Joe Torras, a rancher at Standing Rock, told the AP. "Once you damage that trust, we will never let it go. You only get one shot."

"We all thought a lot about Heidi, but I believe she betrayed our people," Char White Mountain, who voted for Heitkamp in 2012, told the AP. "We really needed someone we could trust."

Even former Standing Rock Chairman David Archambault, who was in office during the often violent protests against the pipeline, couldn't bring himself to cover for Heitkamp.

"I think she was caught in the middle. But when her hand was forced, she chose the pipeline," he said. "She always said she supported Indian Country, but when all of Indian Country from across the nation was at Standing Rock - she didn't show up."

In 2012 Heitkamp's margin of victory was exactly 2,936 votes.

As Heitkamp aligns herself with Trump and traditionally Republican positions on issues like energy, can she really count on getting enough right-of-center voters to replace the left-of-center voters she inspires to stay home?

Rob Port, founder of SayAnythingBlog.com, a North Dakota political blog, is a Forum Communications commentator. Follow him on Twitter at @RobPort