Shares of Sweden's Volvo Cars tumbled as much as 19% on Thursday morning, putting the company on track for its worst trading day ever. The automaker, which is owned by China's Geely Holding, posted a substantial drop in fourth-quarter operating profit, citing the impact of U.S. tariffs, negative currency effects and weak demand. Volvo Cars said fourth-quarter operating income excluding items affecting comparability fell by 68% to 1.8 billion Swedish krona ($200.46 million) compared to the same