State Sen. Kelly Armstrong declared his candidacy for Congress Thursday amid an already crowded slate of Republicans.

Speaking in Bismarck on a three-city tour, the Dickinson attorney pledged to be a "fighter" for North Dakotans in the U.S. House of Representatives, adding that he won't run in June's primary election if denied the Republican endorsement at April's convention. Armstrong resigned Tuesday as the state Republican party chair.

"Our bylaws require that if you run for statewide office you have to resign," he said. "Anybody who knows me knows I'm a party-first guy."

Armstrong told reporters he doesn't begrudge other candidates for continuing to the primary: "I can’t resign as party chair on Tuesday and tell the party I don’t care about their rules on Thursday .... At the end of the day, I'm going to finish this thing with my principles and my integrity. The hypocrisy of that is something that is beyond me.

"It's convention or bust."

Regarding the packed field of Republicans seeking the state party's endorsement for Rep. Kevin Cramer's seat, Armstrong pointed to the party's strength in the state but disputed some candidates' seriousness.

"We can argue about how legitimate some of those other candidates are, I guess, but the answer is we have a robust party in the state with supermajorities," he said. "It's awesome to give everybody choices."

Armstrong joins U.S. Marine Corps veteran Tiffany Abentroth, state Sen. Tom Campbell, R-Grafton, DuWayne Hendrickson and Paul Schaffner, both of Minot, in the Republican race.

Campbell, who declared his U.S. Senate campaign in August, joined the House race last week following Cramer's announcement for Senate. In a statement, campaign spokesman Mike Schrimpf said Campbell is the "best positioned" candidate.

"He’s spent months criss-crossing the state to meet voters, and Republican voters know that no one will work harder to fight for conservative values," Schrimpf said. "Tom’s a Washington, D.C., outsider who will partner with Donald Trump to push the president’s conservative change agenda through Congress."

"Tom’s been working really hard, and I’m going to stand on my record and I’m going to do everything I can to convince delegates for our state convention to vote for me," Armstrong said Thursday.

Hendrickson and a spokeswoman for Abentroth did not return messages for comment Thursday after Armstrong's announcement.

"We'll see how he campaigns," Schaffner said.

Armstrong told his crowd he plans to build on "the momentum" from President Donald Trump's administration if elected to the U.S. House, which he said he views as "just more my style" and "scrappier."

"Now is the time for D.C. to get serious about balancing the budget, just like we do in North Dakota," he said, also noting issues of addiction, law enforcement and support for farmers and ranchers.

Armstrong was first elected in 2012.

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