U.S. stocks are falling Thursday, led by AI superstars that are now feeling the painful downside of big expectations. The S&P 500 was down 0.7% in morning trading, resuming its slide after a mini-recovery from the prior day helped it claw back some of its sharp drop over recent weeks.

The tariffs between the U.S., China, Canada and Mexico prolonged global market turbulence as Trump threatened retaliatory tariffs on Canada.