“Now both sides have reached consensus in many respects, but frankly there are also areas of disagreement,” he said. “We believe that these are major matters of principle, and any country has its own important principles — we can’t make concessions on matters of principle.”

Despite punishing tariffs already on nearly half of Chinese exports to the United States, Beijing is still resisting many of the most significant changes that the administration seeks. It has been reluctant to roll back subsidies for advanced manufacturing industries or to make public commitments to stop cybertheft.

Instead, a trade deal between the two countries seems more likely to bring change around the margins — tens of billions of dollars of soybean purchases, some tariffs lifted and changes to the text of Chinese laws or regulations that the country might ultimately disregard, particularly once another administration occupies the White House.

“This is a decades-long endeavor,” said Robert Daly, the director of the Wilson Center’s Kissinger Institute on China and the United States. “This can’t be waved away over cake at Mar-a-Lago.”

The notion that the United States has one last shot to change China’s behavior is held by an array of people on both sides of the political spectrum. But it is an aggressive notion of American power to upend a rival system that has delivered prosperity for its people and put China on course to be the world’s largest economy.

Many in China see the United States as a declining power bent on enforcing its will on a world that no longer cowers before its hegemonic might. The troubles in American democracy and the long economic slump after 2008 persuaded many in China that its instincts to chart its own course were correct. In the eyes of many Chinese, their country is simply reclaiming its historic status as a dominant regional power in Asia.

It has also projected power across Asia, Africa and elsewhere while the United States has, on many fronts, retreated from its post-World War II commitment to the global order. But it has done so with little application of military force, in sharp contrast to what many in China see as American militarism.