California's 4th Congressional District holds its nonpartisan top-two primary on June 2, 2026, with longtime incumbent Mike Thompson facing Democratic challenger Eric Jones alongside several Republican candidates. Redistricting added rural territory from counties such as Colusa, Placer, and Yuba, yet the seat retains a strong Democratic lean. Thompson's decades of incumbency, established fundraising, and moderate profile have positioned him as the frontrunner, while Jones has invested substantial personal funds in an effort to mobilize younger voters. No significant developments have altered the candidate field since the March filing deadline, leaving the outcome dependent on voter turnout among Democratic-leaning blocs in the final days before the vote.