Mr. Xi will face internal difficulties in coping with Mr. Trump’s aggressive threat. He risks weakening his position if he is seen as giving in to American demands, especially in areas where many people in China feel the country has to make progress, such as in technology, if it wants to keep growing at a healthy pace.

In fact, Chinese internal politics may be at the root of the sudden hitch in the trade talks.

The Trump administration has reacted much more strongly than the Chinese government expected it to, an issue that came up in negotiations last week in Beijing between senior Chinese and American officials, the people familiar with the trade talks said. That was when Chinese negotiators said any concessions in the trade agreement would need to be done through regulatory and administrative actions by the Chinese government, and not cemented in place through actual changes in Chinese law through the country’s legislature.

Foreign critics have long derided China’s legislature, the National People’s Congress, as a rubber stamp for the Communist Party. Bills backed by top leaders are approved by overwhelming majorities, often with only a handful of votes against them. But top leaders also do a lot of back-room maneuvering before any bill is introduced. Sometimes the maneuvering goes on for years without a consensus being reached. The congress also meets only once a year, making it difficult to get legislation approved quickly.