Rep. Kevin Hern (R-OK) won the Oklahoma Republican Senate primary on June 17, 2026, positioning him for a likely victory in the general election in November. Hern, who received an endorsement from former President Donald Trump, was favored to defeat multiple GOP challengers and will compete against the Democratic nominee for the Senate seat previously held by Markwayne Mullin, now the Secretary of Homeland Security.
Mullin, who was confirmed to his role in March, was a first-term senator and had previously served in the House. Oklahoma Governor Kevin Stitt appointed Sen. Alan Armstrong (R-OK) to fill Mullin's vacancy, but state law prohibits Armstrong from running for election to the position.
Due to state law, the winner of the November election will assume office immediately. The seat is expected to remain under Republican control, with other open seats in states such as Montana, Louisiana, Kentucky, Alabama, and Wyoming. Several candidates are competing for Hern’s current seat in Oklahoma’s 1st Congressional District, which includes Tulsa. Trump-endorsed pastor Jackson Lahmeyer is among those running, facing four other candidates. If no candidate secures more than 50% of the vote, a runoff will occur on August 25.