California's 4th Congressional District holds its nonpartisan top-two primary on June 2, 2026, with the two highest vote-getters advancing to the November general regardless of party. Incumbent Democrat Mike Thompson, a longtime moderate seeking his 15th term, faces a primary challenge from fellow Democrat Eric Jones amid new district lines drawn under Proposition 50 that added rural and historically conservative areas while shifting the overall partisan balance toward Democrats. Multiple Republican candidates, including nurses Sharon Brown and Mandy Ghusar, are also on the ballot. The race occurs just days before voting begins, with early ballots already distributed and in-person early voting available.