U.S. stocks sank in another dizzying day of trading Thursday after U.S. President Donald Trump promised stiff tariffs on imported steel and aluminum, worrying investors about possible retaliation by other countries. The Dow Jones industrial average fell 420.22 points, or 1.68 percent, to 24,608.98, the S&P 500 lost 36.16 points, or 1.33 percent, to 2,677.67 and…