Scott Horsley

But late this week came a reminder that the world's two biggest economies are not on a friendly footing.

Beijing imposed new export restrictions on vital rare earth materials.

And President Trump reacted angrily, threatening to impose a new 100 percent tariff on imports from China next month.

Trump also threatened to cancel an upcoming meeting with Chinese President Xi Jinping.

The reaction from investors was swift and sour.

For the week, the S&P 500 index fell 2.4 percent, the Nasdaq dropped 2.5 percent, and the Dow tumbled nearly 2.75 percent.

Scott Horsley, NPR News, Washington.

Investors had begun to shrug off the trade tensions between the U.S.

and China, even though double-digit tariffs remain in place.

But late this week came a reminder that the world's two biggest economies are not on a friendly footing.

Beijing imposed new export restrictions on vital rare earth materials.

And President Trump reacted angrily, threatening to impose a new 100 percent tariff on imports from China next month.

Trump also threatened to cancel an upcoming meeting with Chinese President Xi Jinping.

The reaction from investors was swift and sour.

For the week, the S&P 500 index fell 2.4 percent, the Nasdaq dropped 2.5 percent, and the Dow tumbled nearly 2.75 percent.

Scott Horsley, NPR News, Washington.

President Trump posted his threat on social media after China imposed new restrictions on exports of rare earth materials.

Trump described that as a hostile act that could clog commercial flows around the world.

Trump said he'd been planning to meet with Chinese President Xi Jinping later this month at an Asia-Pacific summit in South Korea, but he warned that meeting could be scrapped now.

In addition to a 100% increase in tariffs next month, Trump warned he could hit back at China with export restrictions of his own.