and this evening he fired right back with another tariff hike of his own. he also took aim at the fed chair. his harshest attack yet, tweeting, who is our bigger enemy, jay powell or chairman xi? the markets responding in real time. the dow closing down 623 points. all of this as president trump prepares to leave for the g-7 summit in france. here's kyra phillips. >> reporter: wall street today sent reeling after a morning tweet storm from president trump. the dow diving 623 points after the president tweeted american companies were, quote, hereby ordered to stop doing business with china. the president has no authority to order private businesses to cut ties with china. and then he took to twitter again, later in the day, to joke about the stock market plunge. for american farmers like gregg hora in iowa, none of this is funny.