STANDING ROCK SIOUX RESERVATION, N.D. (AP) — Standing Rock Sioux tribal member Marlo Hunte-Beaubrun went door to door on North Dakota's largest American Indian reservations in 2012 turning out the tribal vote to help put Democrat Heidi Heitkamp in the U.S. Senate. Six years later, with Heitkamp fighting hard to win a second term, Hunte-Beaubrun is staying on the sidelines.

She is among Indian voters who say they've lost their zeal for Heitkamp over her perceived non-stance on the Dakota Access pipeline, which brought thousands of American Indians and others to the state in 2016 and 2017 to protest its construction under the Missouri River, just outside Standing Rock.

"It was really a kick in the stomach," Hunte-Beaubrun said. "We rallied so hard for her, but when her hand was forced she basically sold out to big oil."

Democrats' hopes to capture the Senate depend heavily on Heitkamp, who has trod a careful path on energy and other issues to win office and remain popular in a deeply conservative state. But she faces a stern test from the state's lone U.S. House member, Republican Kevin Cramer, in a race seen as a top pickup chance for Republicans.

Heitkamp's first victory came by fewer than 3,000 votes, and American Indians, who tend to vote Democratic, were a source of strength. Three counties with majority Indian populations — Sioux, Rolette and Benson — backed Heitkamp by a more than 4,000-vote margin over then-U.S. Rep. Rick Berg. In Sioux County, home to the Standing Rock reservation, Heitkamp took 83 percent of the vote.

Once in the Senate, Heitkamp earned respect from American Indians for her knowledge of issues important to them, such as domestic violence in Indian Country and the relationship between tribal governments and the federal government. The first bill she introduced established a commission to study the challenges facing Native American children, an issue she had pursued since the 1990s when she was North Dakota's attorney general.

Then came the Dakota Access pipeline, a $3.8 billion project by Texas-based Energy Transfer Partners to move oil from North Dakota's rich Bakken fields to a shipping point in Illinois. The pipeline offered oil companies a cheaper way to get their product to market, was seen as safer than rail shipping and had the support of most state leaders.

The Standing Rock tribe opposed it as a threat to water. Their protest grew into a national event for environmental advocates, and pipeline opponents frequently clashed with police. In the ensuing months, Heitkamp's public statements didn't take a position on the pipeline, instead typically urging courts and federal officials to resolve uncertainty around the project while supporting protesters' right to demonstrate.

On Standing Rock, a 3,600-square-mile reservation that straddles the Dakotas border, there are few industries besides a casino. The reservation is home to about 10,000 people, and unemployment runs as high as 20 percent. In several interviews, some residents remained loyal to Heitkamp and said they would support her. Others said they were disappointed and would not.

"The majority of the people here feel the same way I do — she chose oil over Indians," said Joe Torras, a 57-year-old rancher and horse trainer at Standing Rock. "Once you damage that trust, we will never let it go. You only get one shot." Torras said he isn't planning to vote in November.

In an interview with The Associated Press, Heitkamp highlighted her work on Indian issues, saying no one in the delegation has been a "stronger advocate." Of the pipeline, she said: "My interest was keeping everybody safe."

"When you look at the choices you make in this job, not everybody always is going to agree with you," Heitkamp said. "I will continue to work on things we can all agree on."

Char White Mountain, a 67-year-old retired office administrator and great-grandmother, said she voted for Heitkamp previously but won't again. She would never vote for Cramer, who strongly supported the pipeline, and said she will probably just stay home on Election Day.

"We all thought a lot about Heidi, but I believe she betrayed our people," said White Mountain. "We really needed someone we could trust."

Mary Louise Defender Wilson, 87, a writer and retired educator, said Heitkamp was in a no-win situation on a pipeline protest that she said was hijacked by outsiders.

"I think she was right not saying anything about that pipeline — there were some really bad things that happened there and it distracted from our real issues," Defender Wilson said. She campaigned for Heitkamp six years ago and will again, planning to hand out brochures and post yard signs at her home in Porcupine, a tiny community of fewer than 150 people on Standing Rock.

Former Standing Rock Tribal Chairman Dave Archambault, who was the face and voice of the fight against the Dakota Access oil pipeline, said he met with Heitkamp when the pipeline was first proposed and long before the protests "to let her know this was going to be an issue for us."

"I think she was caught in the middle. But when her hand was forced, she chose the pipeline," Archambault 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."

"She didn't truly listen to what Indian Country was saying," Archambault said. "Now she's in a bind."