Representative Don Bacon of Nebraska, a mainstream Republican, on Tuesday easily fended off a primary challenge from a right-wing businessman, advancing to what is expected to be a tight re-election contest in a competitive district won by President Biden in 2020.

Mr. Bacon, a fourth-term congressman who has maintained a reputation as an independent voice in a party increasingly dominated by the hard right, won with an overwhelming share of the vote, according to The Associated Press.

In recent years, a number of mainstream Republicans in politically competitive districts have been felled in primaries by ultraconservative candidates who went on to drag the party down in the general election.

But since he was elected in 2016, Mr. Bacon, a former brigadier general in the Air Force, carved out a niche for himself as one of the only Republicans who could hold the Omaha-based swing seat. Since 2000, voters in the district have backed the winner of the presidential election, except in 2012.

That brand came through for him on Tuesday night.

His opponent, Dan Frei, a hard-line Republican who secured the endorsement of the state’s Republican Party, had painted Mr. Bacon as a fixture of the Washington establishment and ran on cutting federal spending and an “America First agenda.” Mr. Frei described himself as “a Trumper” but did not ultimately secure an endorsement from the former president.

He also lagged far behind Mr. Bacon in fund-raising.

Mr. Bacon, 60, has broken repeatedly with his party to support several bipartisan pieces of legislation, including Mr. Biden’s infrastructure bill, a bill to establish an independent commission to investigate the Jan. 6 attack on the U.S. Capitol, and a measure calling for the repeal of the Defense of Marriage Act.

He was one of several Republicans in purple districts who pressed Speaker Mike Johnson to allow a foreign aid package including funding for Ukraine to come to a vote on the House floor. “We need to have a Churchill, not a Chamberlain,” Mr. Bacon said at the time.

Mr. Frei sought to weaponize Mr. Bacon’s support for aid to Ukraine against him; Mr. Bacon, in turn, received backing from Mark Levin, a prominent right-wing radio host.

“I am not into these radical isolationists,” Mr. Levin said. “I don’t side with terrorists against Israel. I don’t side with Russia against Ukraine.”

Mr. Bacon also received some backup from the Congressional Leadership Fund, the super PAC aligned with House Republican leaders, which ran advertisements supporting the congressman on the southern border, an issue his opponent had sought to leverage against him.

Mr. Bacon won re-election last year by 3 points against Tony Vargas, a state senator, even though Mr. Biden won the district in 2020 by 6 points.

He will have a rematch against Mr. Vargas in November.