An ugly day for health-insurer stocks weighed on indexes after news that the Trump administration wants to hold Medicare rates almost flat next year. Humana UnitedHealth Elevance Health and CVS Health were the S&P 500’s four worst performers, all tumbling 14% or more. In all, the health-insurance selloff erased $99 billion in market value across six hard-hit stocks Tuesday, according to Dow Jones Market Data.