US stocks are falling Monday after President Donald Trump took little time to ramp up his newest tariffs, and as investors continue to punish companies that could be losers in the artificial-intelligence revolution. The S&P 500 sank 0.8 per cent after Trump said on Saturday that he would place temporary 15 per cent tariffs on other countries. That's up from the 10 per cent rate he had announced Friday in response to a Supreme Court ruling that struck down his sweeping "reciprocal" taxes on imports from around the world. The Dow Jones Industrial Average was down 659 points, or 1.3 per cent, as of 1:25 pm. Eastern time, and the Nasdaq composite was 0.9 per cent lower. Trump's quick shift toward more aggressive tariffs shows how much uncertainty still hangs over the global economy, even after the Supreme Court said the president lacked the legal authority to institute his sweeping "reciprocal" tariffs. Beyond a 15 per cent tariff that could last for up to 150 days, unless Congress ...