BISMARCK, N.D. — North Dakota Republican state Sen. Tom Campbell said Wednesday that he will end his campaign for the state’s lone U.S. House seat.

Campbell made the announcement at a luncheon in Fargo, which was attended by state Republican Party Chairman Rick Berg and state Sen. Kelly Armstrong, who won the party endorsement over Campbell at last weekend’s state convention.

“In this political environment, it’s critical for Republicans to be united and focused on victory in November,” Campbell said in a statement. “We need to make sure Republicans keep North Dakota’s congressional seat, and I’m confident Kelly will fight for conservative values in Washington.”

Campbell told The Associated Press that he feared “an ugly primary fight” with Armstrong that would only benefit Mac Schneider, the Democrats’ endorsed House candidate.

“I just didn’t want that,” he said.

Campbell filed a petition Monday to run in the June 12 primary despite losing the endorsement, but party officials had been seeking to get him to step aside. Tiffany Abentroth and Paul Schaffner, who also competed for the GOP endorsement, also are continuing to the primary, filings show.

Campbell’s name will still appear on the June primary ballot because his petition Monday has been certified, according to Secretary of State Al Jaeger.

Armstrong got a first-ballot endorsement from delegates with an 847-480 vote over Campbell, a state senator and wealthy potato farmer from Grafton.

Armstrong said Campbell called him Tuesday night to say he was pulling out of the race.

“It’s a tough decision for anyone to make,” Armstrong said. “I think Tom did put the people of North Dakota above himself.”

Armstrong said Campbell’s withdrawal will allow his campaign to “focus our energy on winning in November.”

Campbell raised about $1 million — three-quarters of it from his own pocket — on a Senate campaign starting last summer, only to be effectively forced out when GOP Rep. Kevin Cramer announced he would challenge incumbent Democrat Heidi Heitkamp. The race is seen as critical for control of the closely divided Senate.

Campbell then campaigned for the state’s lone congressional seat, only to be challenged by Armstrong, who stepped down as the state GOP party chairman to run.

Campbell was criticized last month for paying convention registration fees for some delegates. The move is permitted by party rules, but some Republicans — and Armstrong — said it could be seen as vote-buying in an endorsement battle. Though Armstrong had covered a handful of registrations of family members, Campbell had covered far more.

The North Dakota Republican Party said 56 delegates reimbursed the party for registration fees so that their names would not be disclosed.

The party said 52 of the payments were attributed to Campbell and four came from Armstrong.

The state Senate seat for Armstrong is not up for election this year, unlike the state senate seat for Campbell, which is being contested by two Republicans. Campbell did not file to run for re-election to that seat but did not rule out a political office or appointment in the future.

“I’m just going to move on now,” Campbell said. “I will go back if anybody somewhere has an opportunity for me.”