On March 24, 2026, President Pro Tempore Chuck Grassley (R-Iowa) swore Sen. Alan Armstrong (R-Okla.) into the U.S. Senate, filling the vacancy in Oklahoma’s class II seat.
The vacancy began on March 23, 2026, after Markwayne Mullin (R) resigned from the U.S. Senate to serve as the U.S. secretary of homeland security in President Donald Trump’s (R) second term. Oklahoma Gov. Kevin Stitt (R) appointed Armstrong to represent the state in the U.S. Senate on March 24, 2026.
Armstrong is the third person to represent the class II seat since 2020. In the 2020 general election, then-Sen. Jim Inhofe (R-Okla.) won re-election, defeating Abby Broyles (D) 63% to 33%. On Feb. 25, 2022, Inhofe announced that he would resign on Jan. 3, 2023. Ahead of Inhofe’s resignation, Mullin defeated Kendra Horn (D) 62% to 35% in the 2022 special general election for the seat.
As of March 24, 2026, Republicans have a 53 to 45 majority in the U.S. Senate. Additionally, both independent members of the chamber caucus with Democrats.
Vacancies in the 119th Congress
So far in the 119th Congress, there have been nine vacancies in the U.S. House of Representatives and four in the U.S. Senate. Of those vacancies:
- Three in the U.S. Senate were filled via appointment.
- One in the U.S. Senate was filled when Sen. Jim Justice (R-W.Va.) was sworn into office 11 days after the start of the 119th Congress. Justice delayed his swearing-in to fulfill the remainder of his term as governor of West Virginia.
- Six in the U.S. House were filled after special election winners were sworn in.
As of March 24, 2026, three vacancies in California's 1st Congressional District, Georgia's 14th Congressional District, and New Jersey's 11th Congressional District have not been filled.
Congressional vacancies since the 113th Congress
During the 113th through 118th Congresses, there were 88 vacancies in the U.S. House and 16 in the U.S. Senate. The average length of a vacancy in the U.S. Senate during that period was seven days. The average length of a vacancy in the U.S. House during that period was 138 days.
The longest vacancy in the U.S. Senate during that period was in New Jersey. The vacancy occurred during the 118th Congress, when Sen. Bob Menendez (D-N.J.) resigned on Aug. 20, 2024. Following Menendez's resignation, the seat was vacant for 20 days.
The longest vacancy in the U.S. House during that period was in Michigan's 13th Congressional District. The vacancy occurred during the 115th Congress, when Rep. John Conyers, Jr. (D-Mich.) resigned on Oct. 27, 2019. Following Conyers' resignation, the seat was vacant for 359 days.