“We definitely will take whatever necessary countermeasures to protect our fundamental right, and we also urge the United States to come back to the right track in finding the right solution through the right way” said Mr. Zhang, China’s U.N. ambassador.

After a series of missteps and misunderstandings, the United States and China appear to be nowhere close to a trade agreement at a time when trade barriers remain in place with other American partners. Mr. Trump’s rewrite of the North American Free Trade Agreement is still stalled in Congress, awaiting the support of Democrats. His threat of auto tariffs has not yet persuaded Japan or Europe to sign a trade deals with the United States, as he intended. And the European Union, India, China, Turkey and others have responded to Mr. Trump’s aggressive trade tactics by putting their own retaliatory tariffs on American products.

If the president’s newly threatened tariffs go into effect, the United States will have imposed levies on all of the goods it imports from China, which totaled $539.7 billion last year.

Mr. Trump said that the new tariffs would go into effect on Sept. 1, leaving a window for the United States and China to try to work out their differences. But that appears to be a difficult task. Negotiators from the two countries continue to disagree over how the agreement would be enshrined in China’s laws, how many of Mr. Trump’s tariffs on China would be removed, and how many American goods China would purchase.

[You might feel the pinch of this round of tariffs. Here’s how.]

The president and his advisers insist the strategy is necessary to take on China’s long record of unfair trade practices, but the tariffs are taking a toll.

The tech-heavy Nasdaq composite index fell 1.3 percent on Friday, and the Dow Jones industrial average dipped 0.4 percent. The yield on the 10-year Treasury note fell to 1.85 percent, its lowest level since 2016, in a sign of economic pessimism.