After President Donald Trump tapped former Sen. Markwayne Mullin (R-Oklahoma) to replace the fired Kristi Noem as secretary of the U.S. Department of Homeland Security (DHS), Oklahoma Gov. Kevin Stitt appointed Alan Armstrong to temporarily fill the U.S. Senate seat. Oklahoma voters will ultimately decide who holds the seat for a full term — and in the meantime, an "internal fight" among state Republicans is "boiling over" as they "vie to fill the last two months of former Sen. Markwayne Mullin's term," according to Washington Sun reporter Reese Gorman. At stake is who holds the Oklahoma seat for the final weeks of the current Congress.

"The dispute is over when Sen. Alan Armstrong's temporary term ends and the next Oklahoma senator — likely Rep. Kevin Hern — would be sworn in," Gorman reports in the Washington Sun. "Hern wants to be sworn into the Senate in November following the election, while Armstrong wants to stay on through January."

In the general election, Hern is up against Democratic nominee N'Kiyla Jasmine Thomas.

Oklahoma law, Gorman notes, states: "The candidate elected to the office at the regularly scheduled election shall be deemed to also have elected to fill the vacancy and shall be eligible to assume the office upon the official certification of the election by the State Election Board."

"According to multiple sources familiar with the matter," Gorman reports, "Hern's team believes the law would allow Hern — if he wins the election — to be sworn into the Senate in November, as Oklahoma must certify the election within seven days of it being completed. However, Armstrong's team believes the law is less clear and that he was appointed to serve out the remainder of now-Secretary of Homeland Security Mullin's term, which ends in early January. Armstrong wants to stay on at least until legislation on permitting reform gets done, sources tell The Washington Sun. There's a chance that happens in the lame-duck session." Because the two sides disagree on when Armstrong's appointment ends, the fight effectively determines who occupies the seat if Congress convenes for a lame-duck session in which that permitting reform legislation could come up.

Gorman adds, "All this has caused a rift between the two members, sources say."

Hern, according to Gorman, is being represented by Glenn Coffee, a well-known attorney in Oklahoma, while Stitt is "pushing for" Armstrong "to remain in office until January."

The dispute has already moved into formal legal channels. "On September 11," Gorman reports, "an attorney representing Armstrong sent a letter, which The Sun obtained, to Stitt asking that he request the attorney general's opinion on the matter. In the letter, the lawyer says, 'The upcoming Senate election is not intended to determine who will succeed to the few remaining weeks' of the term. Armstrong's attorney said that 'Senator Armstrong seeks an opinion addressing whether his appointment continues until the 120th Congress convenes on January 3, 2027, or terminates immediately upon certification and qualification of a new Senator elected at the upcoming election.'"

Gorman continues, "Multiple sources told The Sun that Stitt has not yet requested the attorney general's opinion on the matter. However, on Tuesday State Senate Pro Tempore Lonnie Paxton requested an opinion from State Attorney General Gentner Drummond on when the next senator would get sworn in." Drummond's opinion, along with the November election and Oklahoma's seven-day certification window, now anchors the timeline for when the seat changes hands.

Gorman shared the report in a post on X.