Incumbent Mike Thompson, first elected in 1998, seeks renomination in California's strongly Democratic 4th Congressional District through the June 2, 2026, top-two primary. The district's partisan composition and Thompson's long tenure have shaped trader expectations that he and Democratic challenger Eric Jones will advance, as multiple Republican candidates including Sharon Brown and Mandy Ghusar trail significantly in visibility and resources. No major developments have emerged since the March 6 filing deadline to alter the candidate field or shift positioning. The primary's proximity leaves little time for late developments to change outcomes before ballots are cast.