Incumbent Democrat Mike Thompson faces a rare well-funded primary challenge from fellow Democrat Eric Jones in California's 4th Congressional District's top-two primary on June 2, 2026, where the top two vote-getters advance regardless of party. Jones slightly outraised Thompson through December 2025 and earned progressive endorsements like Our Revolution, while Thompson secured backing from the California Democratic Party and business groups such as Metro PAC; a fragmented field of six Republicans and one independent likely splits the opposition vote, boosting Democratic advancement odds. The redrawn district leans Solid Democratic (D+17 PVI) but by a narrower margin than prior lines, with no public polling available. Early voting begins May 23, potentially amplifying grassroots efforts like Jones's 100,000+ doors knocked. Recent backlash against Jones in early March underscores intra-party tensions.