UnitedHealth's stock is plunging on higher medical costs. That may mean trouble for more insurers

1. UNH stock fell 20% after a profit forecast cut due to rising medical costs. 2. Higher medical costs signal trouble for Medicare Advantage providers, impacting industry outlook. 3. UNH faces government scrutiny, complicating its Medicare billing practices. 4. Forecasts may improve after Trump administration boosts Medicare Advantage reimbursement rates.