The June 2, 2026, primary for California's 4th Congressional District pits longtime incumbent Mike Thompson against Democratic challenger Eric Jones in a top-two format, where the two highest vote-getters advance regardless of party. Jones, a political newcomer, has matched or slightly exceeded Thompson's fundraising through individual donors and personal contributions, while Thompson draws support from established PACs and state Democratic endorsements. Redistricting under Proposition 50 incorporated additional conservative-leaning counties, modestly narrowing the district's Democratic edge without creating viable Republican paths. A crowded Republican field of six candidates remains fragmented, with minimal fundraising or organizational strength to consolidate support. No recent polls or major endorsements have altered expectations that Thompson and Jones will claim the top two spots, consistent with historical patterns in similar California districts.