It’s never good to be on the receiving end of a withering attack by Donald Trump. That applies equally to people — like Rep. Nancy Pelosi — and companies — like, say, Amazon.

Amazon was created by Jeff Bezos, and the massive company made him a billionaire. With all his extra cash, Bezos decided to move into journalism, buying The Washington Post, a once-great newspaper. Since he bought the Post, the paper has relentlessly attacked President Trump.

So Trump decided to fight fire with fire. He’s tweeted about Amazon — it’s sweetheart deal with the U.S. Postal Service, whether Bezos is really a “lobbyist,” the company’s tax-paying history — and the counter-punching is having a serious effect: Amazon’s stock is down 7% since Trump’s onslaught began. That’s a $37 billion loss in market value.

“The Dow dropped more than 700 points and the Nasdaq plunged 3% on Monday. All three major indexes are now in the red for the year,” CNN reported.

“The sell-off on the first day of the second quarter came after President Trump once again attacked Amazon on Twitter. Amazon (AMZN), one of the biggest drivers of the 2017 market rally, tumbled 5%, wiping out more than $37 billion of its market value.”

Again, note to anyone out there — anyone: Don’t mess with Trump. It never pays off in the end.