https://cdnph.upi.com/ph/st/th/7501784655370/2026/upi/119fa3a9525e1b5d2f68419a66338e2a/v1.5/Deaths-resignations-in-Congress-test-narrow-majority.jpg" /> An explainer of how vacant U.S. House and Senate seats are filled when a lawmaker resigns or dies during their term, highlighting state laws.