Among the most difficult questions still on the table are the so-called structural issues that are at the core of the Chinese economic model. These include subsidies and other financial assistance provided to state-owned businesses, which make them unfair competitors. So far, China has reportedly agreed to more transparency on subsidies, an important first step, but there has not been enough progress on controlling them. Mr. Trump will need more than that to placate his political base. The president of the A.F.L.-C.I.O., Richard Trumka, has already warned, in a recent interview with The Financial Times, that he will consider any deal that fails to reduce industrial subsidies “inferior.”

Even if they can address the structural issues, the United States and China must still decide how the deal would be enforced. In particular, they have not agreed on whether tariffs could be reimposed if violations occur. The United States is demanding that it retain the right to use unilateral tariffs, while China gives up its right to retaliate. That is a tough sell politically for Beijing, and so far neither side appears to be budging.