In California's 4th Congressional District top-two primary on June 2, 2026, incumbent Democrat Mike Thompson faces a competitive challenge from well-funded Democrat Eric Jones, who has raised $2.6 million compared to Thompson's $2 million through late 2025, bolstered by Our Revolution endorsement and appeals to younger voters on affordability and corporate accountability. Thompson holds Democratic Party of California backing and emphasizes his long tenure on the House Ways and Means Committee, wine industry support, and wildfire relief. A fragmented Republican field of six candidates with minimal fundraising likely advances one GOP contender alongside a Democrat, per historical patterns in this D+17 district. Early voting begins May 4; recent forums, including Jones winning a March 30 Indivisible Yolo straw poll, signal intensifying Democratic vote-splitting risks.