Incumbent Democrat Mike Thompson faces Democratic challenger Eric Jones and several Republican candidates in California's June 2 top-two primary for the 4th Congressional District. The solidly Democratic district, with its strong partisan lean, favors both leading Democrats advancing under the state's top-two system. Thompson's long tenure since 1999 and substantial campaign resources contrast with Jones's self-funded effort and endorsements from progressive groups. Republican candidates remain fragmented with limited fundraising, reducing their chances of placing in the top two. No major developments have shifted the field since the March filing deadline, leaving fundraising totals, voter turnout patterns, and the district's electoral math as primary factors in trader assessments ahead of the vote.