In California's 4th Congressional District top-two primary on June 2, 2026, incumbent Democrat Mike Thompson faces primary challenger Eric Jones, a well-funded progressive businessman who has raised more than Thompson as of late March, while six Republicans and one independent fragment the GOP vote in this safe Democratic seat reshaped by 2025 redistricting. The Sacramento Bee endorsed Thompson on May 3 for his decades of experience on local issues like agriculture, water rights, and taxes, contrasting Jones's relative inexperience amid minor backlash earlier this year. Mail ballots began arriving May 4, with voter registration closing May 18 and voting centers opening May 23; top two vote-getters advance to November regardless of party, potentially pitting both Democrats against each other if Republicans split.