In California's 4th Congressional District top-two primary on June 2, 2026, incumbent Democrat Mike Thompson faces a well-funded primary challenge from Eric Jones, another Democrat endorsed by Our Revolution and emphasizing economic opportunity and anti-corruption reforms. Both lead in fundraising—Thompson with $2.6 million cash on hand and Jones $1.5 million as of late March—while six Republicans and one independent risk splitting the conservative vote in this Solid Democratic-leaning district reshaped by recent redistricting to narrow its Democratic margin. No public polls have emerged, but the fragmented GOP field boosts chances of both Democrats advancing to November. Voter registration closes May 18, with mail ballots mailing soon after.