Markets tumbled after President Trump unveiled his plan to impose tariffs on America's trading partners, causing the S&P 500 to fall 4.8 percent, its worst day since 2020. Economists warn that the tariffs will raise prices for American consumers and lead to a pullback in hiring. The E.U. and China have vowed to retaliate, while Canada has already placed a 25 percent tariff on American-made cars and trucks. American allies in Southeast Asia, such as Vietnam, Thailand, and Cambodia, will also face punishing tariffs.