Eight years ago, when a newly elected Donald J. Trump promised to apply the powers of the Oval Office to start a trade war with China, the target of his ire was widely viewed as a juggernaut. China was the indispensable factory floor to the world and a swiftly developing market for goods and services.

As Mr. Trump now prepares for his second stint in the White House, he is vowing to intensify trade hostilities with China by imposing additional tariffs of 60 percent or more on all Chinese imports. He is pressuring a country that has been chastened by a powerful combination of overlapping forces: the calamitous end of a real estate investment binge, incalculable losses in the banking system, a local government debt crisis, flagging economic growth and chronically low prices — a potential harbinger of long-term stagnation.

The decline of fortunes at home has made Chinese companies especially focused on sales abroad. And that makes the country vulnerable to any threat to its export growth, a weakness that would enhance the expected pressure from the Trump administration as it plans to seek a deal that would increase Chinese purchases of American goods.

“The balance of power has certainly shifted in favor of the United States,” said Eswar Prasad, a professor of trade policy at Cornell University who was previously the head of the China division at the International Monetary Fund. “The Chinese economy is not quite on the ropes, but it has been struggling for a while.”

Yet complicating factors beneath that widely shared assessment may strengthen China’s ability to endure whatever measures the incoming Trump administration may have in store.