Progressive challengers shake up Democratic primaries in 2026 race

Melat Kiros toppled Rep. Diana DeGette in Colorado’s Denver-area Democratic primary, ending DeGette’s 29-year hold on the seat and giving progressives one of their biggest victories of the 2026 season. The upset landed as Democrats weighed whether their primaries are producing a newer, more confrontational party or simply punishing incumbents who have been in Washington too long.

Colorado’s June 30 ballot also drew unusual attention because it included a closely watched Senate contest, even though Sen. Michael Bennet is not scheduled to face voters again until 2028. The fight was less about that seat than about the mood of Democratic primary voters, who are being asked to choose nominees in 35 states for the Senate and in all 50 states for the House before the November 3 general election.

The Colorado shock followed another warning sign in New York City. Ahead of the June 23 primary there, Zohran Mamdani endorsed a democratic socialist challenger to Rep. Adriano Espaillat, adding to the sense that the party’s left flank is willing to challenge entrenched Democrats in high-profile races. Centrist Democrats have been unnerved by the pace of those wins, and the reaction has sharpened as more primaries approach.

The scale of turnover is already large. AP’s congressional retirements tracker shows 62 current House members, including 24 Democrats and 38 Republicans, will not return next term as of July 1. That leaves a broad opening for new candidates while also making each primary test more consequential for the party’s direction.

The June results in Colorado, New York and Maine have become an early read on how Democrats are sorting through ideology, electability and generational change. For incumbents, the danger is no longer limited to heavily anti-establishment districts. It now reaches long-held seats, high-profile names and primaries that can flip quickly when activists, younger voters and progressive challengers converge on the same race.