The Dakota Access Pipeline (DAPL) has been in operation for more than a year, but ghosts of the protests still linger for Sen. Heidi Heitkamp, who is struggling to hang on to her seat as the lone Democrat in North Dakota’s congressional delegation. A new ad released by the North Dakota Republican party calls the senator out for failing to come out strongly in support of law enforcement during the protests.

“Dangerous radicals terrorized our state during the DAPL protests, setting fires, hurling dangerous explosives–and Heidi Heitkamp did nothing,” the ad says, before a describing the violence that erupted during the protests.

The ad is the latest salvo fired in a race that Heitkamp seems to be losing. From the start, Republicans were given good odds of flipping this Democratic senate seat in a state that Donald Trump won by 36 points. A poll released this week by Strategic Research Associates and NBC North Dakota News found that Heitkamp trailed her opponent, Congressman Kevin Cramer, by 10 points.

Cramer has a long record of supporting domestic energy production, even serving as an advisor on the issue for the Trump campaign. Meanwhile, Heitkamp is trying to split the difference, defending her response to the DAPL protests without alienating voters on the state’s Native American reservations.

“That might be one of the most consequential television ads of the 2018 election cycle. Even defending herself from it is going to be hard,” says Rob Port, a North Dakota political columnist. “If she comes out forcefully against the protests, she’s going to alienate the Native American vote she needs to win. If she goes silent about this criticism, or is in any way perceived as condoning the protests, she’s going to lose votes in the rest of the state.”

The senate Democrat tried to finesse the DAPL issue, condemning the violence by some protesters while urging the Obama administration to move the process forward more quickly.  Heitkamp’s response to the DAPL protests has already caused friction with Native American voters, who were a key to her election in 2012. They see her failure to take a stand during the pipeline protests as a betrayal.

“The majority of the people here feel the same way I do — she chose oil over Indians,” Standing Rock Sioux citizen Joe Torras told the AP earlier in the year. “Once you damage that trust, we will never let it go. You only get one shot.”

Heitkamp’s campaign responded to the new ad by pointing out to NBC News that the senator received an award from the Morton County Sheriff’s office and the Morton County Commission “in recognition of outstanding and dedicated service to the citizens of Morton County during the Dakota Access Pipeline Protest.” However, local observers note that all three members of North Dakota’s congressional delegation received the award, making it more a ‘participation trophy’ than a mark of distinction.

On Wednesday, the North Dakota Democratic-NPL released a poll of its own which was remarkable mostly for what it left out. According to their survey, Heitkamp holds an 18-point lead over Cramer in the state’s eastern cities of Fargo, West Fargo, and Grand Forks, as well as a 14-point lead in the eastern part of the state more broadly. These areas account for about 45 percent of the state’s electorate.

The unusual selection is an attempt to rebut polls showing that Cramer ahead statewide. Also of note is the fact that the focus on the eastern half of the state excludes the area surrounding Mandan and Bismarck, which saw the brunt of the protest activity, and also the Bakken shale region.

Though the signs are favorable for Cramer, still the race is not over. Heitkamp has won tight races before and is popular in the state.  And holding onto this seat is vital to Democrats’ hopes to take control of the U.S. Senate in November.

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