At the same time, tensions with North Korea have risen again, adding to the United States’ need for China’s cooperation in reining in Pyongyang.

Global markets fell again. The S&P 500 notched a fourth consecutive daily decline.

North Korea: The United States seized a North Korean ship for violating American-led sanctions, escalating tensions already on the rise because North Korea has resumed weapons tests.

Trade talks: The sticking point appears to be a late decision by China’s leader, Xi Jinping, to reject demands that China change laws constraining American businesses.

Xi’s tightrope: Mr. Xi must guard his image within China. Ceding to the United States could be humbling, but being hit with new tariffs could shake confidence in his country’s economy.

China’s options: If the United States’ course remains unchanged, Beijing could raise existing tariffs on American goods; encourage Chinese consumers to boycott American products, like iPhones; delay American imports; and let the value of its currency slide.