Incumbent Democrat Mike Thompson faces his strongest primary challenge in years from venture capitalist Eric Jones in California's 4th Congressional District top-two primary on June 2. The district's D+8 partisan lean, reinforced by Proposition 50 redistricting that incorporated additional rural counties while preserving Democratic advantages, sets the stage for both Democrats to advance over a crowded field of six Republicans and one independent. Thompson benefits from 28 years in office, party endorsements, and super PAC support, while Jones leads among challengers through substantial grassroots fundraising from tech donors and a Bernie Sanders endorsement. A splintered Republican vote makes consolidation unlikely, aligning trader consensus with historical patterns favoring incumbents and well-funded opponents in safe Democratic seats. No major polls have emerged recently, but late endorsements or spending could influence the runner-up spot before early voting concludes.