S&P 500 has its worst day since October. Here's why stocks were down.

U.S. stocks closed sharply lower Jan. 20, with the broad S&P 500 index posting its worst day in three months, as investors worried about President Donald Trump's tariff threats in his efforts to take over Greenland. Trump said on Jan. 17 he would impose additional 10% import tariffs on Feb. 1 that will rise to 25% on June 1 on goods from Denmark, Norway, Sweden, France, Germany, the Netherlands, Finland and Great Britain − all already subject to U.S. tariffs and opponents to his plan to acquire Greenland. ...