Worries about President Donald Trump’s tariffs are sending U.S. stocks through sharp swings on Monday as financial markets worldwide drop on concerns about a potential trade war. The S&P 500 was down 0.

Follow the latest news on the tariffs and other Trump administration moves. Leaders for Canada, Mexico, and China, including Justin Trudeau, respond after President Donald Trump imposes tariffs.

Canadian Prime Minister Justin Trudeau announced that Canada would respond with 25% tariffs "against $155 billion worth of American goods."

Donald Trump is the first president to use the International Emergency Economic Powers Act to impose tariffs, teeing up likely legal battles that will test his executive authority.

What to know as President Donald Trump imposes steep new tariffs on imports from Canada, Mexico and China, prompting retaliation and countermeasures.

Just about everyone thought it was a bluff. Top analysts from the biggest banks on Wall Street said it was highly unlikely. Stocks were trading like it wouldn’t happen. Some companies built contingency plans but they weren’t exactly rushing to make changes.