Stocks tumble as Wall Street braces for impact of Trump tariffs. Here's what to know.

Stocks tumbled on Monday as Wall Street braced for the impact of steep new tariffs ordered by President Trump, with mounting fears the new import duties could spark a trade war that could crimp corporate profits and dampen consumer spending.

The Dow Jones Industrial Average shed 421 points, or 1%, to 44,123 in early morning trading. The broad-based S&P 500 lost 1.5%, while the tech-heavy Nasdaq composite index tumbled 1.8%. 

On Saturday, Mr. Trump signed an executive order that imposes 25% tariffs on imports from Canada and Mexico, while adding an additional 10% levy on goods from China. Hours later, Canada responded with retaliatory tariffs of its own, while Mexico said it was also planning to issue tariffs on the U.S. as well, adding to the potential fallout from a trade war with two of the U.S.' closest trading partners.