Business leaders said the result could be a flurry of fire sales at greatly reduced prices as companies from other countries snap up American business interests.

Peter Baum of Baum-Essex, a firm that makes products like umbrellas for Costco and cotton bags for Walmart, said he had already moved much of his manufacturing to factories in Vietnam and Cambodia over the last year because of Mr. Trump’s tariffs.

As the trade war shows up in American cash registers, stock markets and retirement account statements, American shoppers and retirees will grow angry, Mr. Baum said.

“Both Trump and Xi have backed themselves into such a corner that this will go on through the U.S. election,” he said. “These two guys don’t realize that this could cause a global depression, not recession.”

In raising the possibility of an American withdrawal on Friday, Mr. Trump framed it not as a request but as a dictate he had already issued.

“Our great American companies are hereby ordered to immediately start looking for an alternative to China, including bringing our companies HOME and making your products in the USA,” he wrote on Twitter.

In fact, aides said, no order has been drawn up nor was it clear one would be. For the moment, they said Mr. Trump was signaling American businesses to begin to disentangle from China on their own.