The Dow Jones Industrial Average plunged more than 600 points Friday after the latest escalation in the trade war between the U.S. and China rattled investors. The broad sell-off sent the S&P 500 to its fourth straight weekly loss.

Stocks tumbled after President Donald Trump responded angrily on Twitter following China's announcement of new tariffs on $75 billion in U.S. goods. In one of his tweets he "hereby ordered" U.S. companies with operations in China to consider moving them to other countries — including the U.S.

Trump also said he'd respond directly to the tariffs — and after the marke...