Incumbent Mike Thompson faces a Democratic primary challenge from self-funded Eric Jones in California’s 4th Congressional District ahead of the June 2 top-two primary. The district’s strong Democratic lean, reinforced by voter registration and prior election results, favors both Democrats advancing over the field of six Republicans and one independent. Jones has drawn notable attention through substantial personal spending and an endorsement from Bernie Sanders, while Thompson benefits from decades of incumbency and established fundraising. No major developments have shifted the candidate field since the March filing deadline, leaving the outcome dependent on primary turnout and vote consolidation among Republican contenders.