Incumbent Democratic Representative Mike Thompson, who has held the seat since 1999, faces a primary challenge from Eric Jones in California's June 2, 2026, nonpartisan primary for the 4th Congressional District. The race occurs in a heavily Democratic district altered by redistricting under Proposition 50, with Thompson maintaining strong institutional support and name recognition while Jones, a venture capitalist and political newcomer, has out-raised the incumbent in recent fundraising. Multiple Republican candidates, including Sharon Brown and Ray Riehle, are also on the ballot, though the top-two advance system favors Democratic frontrunners in this D+50 environment. No major late developments have shifted positioning ahead of the primary.