Redistricting under California Proposition 50 combined portions of the prior districts held by Republican incumbents Young Kim and Ken Calvert into the new CA-40, forcing a rare same-party general election matchup on November 3. Calvert led the June top-two primary with stronger Inland Empire support, while Kim posted a fundraising advantage exceeding $10 million and benefits from name recognition in Orange County portions. The race has featured heavy negative advertising and outside spending exceeding $11 million, including attacks on Kim tied to past donor scrutiny. These factors, alongside Democratic primary turnout patterns that could influence crossover or abstention effects in the Republican-leaning district, have kept implied probabilities tight in trader markets, with limited recent polling leaving room for late shifts based on turnout or final messaging.