Dustin Peyer, a firefighter, is expected to formally announce his campaign against Heitkamp on Thursday at a marijuana reform rally at the state capitol in Bismarck.

"I'm running for Senate against Heidi Heitkamp. Basically, in my opinion, on the Dem side we have a really boring primary and we can't allow that to happen anymore," Peyer told North Dakota radio station WDAY.

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Pressed about why he is challenging Heitkamp, Peyer pointed to a "Medicaid for all" system and campaign finance reforms.

"Her specifically in my opinion like I say campaign finance reform," he said. "She's in there with everyone else and that's a big part of it. And we need to make sure that she's being accountable and having debates and having town halls."

Asked if he was running just so Heitkamp had a primary opponent, Peyer added that it "kind of started that way" but noted some voters are also unhappy with Heitkamp's support for some of Trump's nominees.

"As more people come out and say they're going to support me, it's really changing. You start looking at the, you know, there are people who aren't convinced on the way she voted on Trump's nominees," he told the radio station.

Progressives have demanded that Democrats draw a hard line against Trump's agenda, including threatening to primary senators who work with the administration.

Referring to Sanders's supporters during the 2016 election, Peyer argued that "those people need a voice."

"That's what I'm trying to represent, the people that came and showed up and let's give them a candidate," he said.

Peyer will face uphill battle against Heitkamp, who was the first Democrat to win in a statewide race in North Dakota since 2008.

Heitkamp hasn't formally said she will run for reelection in 2018, but reportedly raised $1.6 million during the first fundraising quarter of 2017.