These smaller companies, which often have thinner profit margins and less negotiating power with suppliers and customers, could be poorly positioned to handle the next round of tariff increases.

“The escalation of tariffs is creating these problems that corporate America is going to have to work around,” said Lori Calvasina, head of United States equity strategy at RBC Capital Markets. “It’s just going to be tougher for the smaller guys.”

For now, stock investors continue to sit on sizable gains. The S&P 500 remains up more than 12 percent in 2019. But the sell-off also shows Wall Street is factoring in the prospect that the trade fight drags on, even as it closely monitors comments from officials in Beijing and Washington.

On Monday, anxiety about the economy appeared in other financial markets too.

Prices dropped for soybeans and copper, both of which are sensitive to global growth and trade. Interest rates rose in corporate bond markets, an indication that investors were seeking higher premiums in response to the increased risks of a worsening trade fight.

In the stock market, the damage required less interpretation. Shares of companies particularly dependent on trade with China, including semiconductor makers that rely on production networks in the country, fared badly.

Apple, which counts China as a major market for the sale of its iPhone and other devices and leans heavily on Chinese suppliers to produce them, fell 5.8 percent.