With just a few angry tweets, President Trump managed to tank the U.S. stock market. On Friday, Trump escalated his trade war with China, tweeting: “Our great American companies are hereby ordered to immediately start looking for an alternative to China, including bringing … your companies HOME and making your products in the USA.”

As soon as the message hit Twitter, U.S. stocks and Treasury yields sank, CNBC reported. The Dow Jones Industrial Average was down about 1.7% shortly after midday, according to Barron’s, while the S&P 500 dropped 1.8%, and the Nasdaq Composite was down 2.2%. CNBC notes that tech stocks were hit particularly hard, with Apple shares dropping 4.1%, VanEck Vectors Semiconductor ETF (SMH) down 3.7%, and Nvidia and Broadcom tumbling around 5%.

The timing couldn’t have been worse. The president’s tweets came just as markets had begun to recover from earlier losses thanks to a soothing speech made by Federal Reserve Chair Jerome Powell at the annual central banking symposium in Jackson Hole, Wyoming. As soon as Powell managed to calm investors’ fears, Trump’s tweets stoked them again. The timing may have been intentional, as Trump name-checked Powell in his tweetstorm, calling him an “enemy.”