U.S. — Ken Paxton defeated John Cornyn in the Republican primary for Texas Senate on May 26, 2026. Cornyn received 37% of the vote in the runoff. The loss marked the first time a fourth-term senator lost a re-election bid in the 21st century.

Lindsey Graham of South Carolina received 56% of the vote in his primary. Most senators who faced primaries in the 2026 cycle either won with over 60% of the vote or were uncontested.

Since 2000, 16 senators running for a fourth term or higher have lost re-election bids. Nine were Democrats and seven were Republicans. Eleven lost bids for a fourth term, two lost bids for a sixth term, one lost a bid for a fifth term, and one lost a bid for a seventh term. Richard Lugar, who sought a seventh term, lost his re-nomination bid and was the longest-serving senator defeated in a primary or general election since 2000.

William Roth was defeated by Tom Carper in the 2000 general election during Roth's campaign for a sixth term. Roth was the longest-serving senator to lose a general election since 2000. Since 2000, five senators who served three or more terms have lost their primary bids for re-election. Joe Lieberman lost his primary bid for re-election after serving three or more terms and subsequently won a third-party campaign.

Seven senators who have served for three or more terms are running for re-election in the 2026 cycle. Susan Collins and Jack Reed are the longest-serving senators among this group, both seeking a sixth term. If Collins wins re-election, she would become the longest-serving senator in Maine history. If Reed wins re-election, he would tie Clairborne Pell for Rhode Island's record for longest service.

Collins is the only senator in her third term or higher running for re-election in 2026 in a race considered a toss-up by media outlets. Sabato's Crystal Ball and The Cook Political Report with Amy Walter rated the Maine Senate race as Likely Republican prior to Cornyn's defeat. Collins is also the only Republican Senator up for re-election in 2026 in a state that Kamala Harris won in 2024. Reed has not yet faced a primary; Rhode Island's primary is scheduled for September 9, where Reed and Connor Burbidge are running.