For two decades, American politicians have been escalating their rhetoric about how to confront a rising China, one that grabs territory in the South China Sea, vacuums up American jobs and mounts cyber attacks on the United States.

But now both Republicans and Democrats face a different challenge: how to deal with a weakening China, whose behavior may be as aggressive as always, but whose faltering market poses an entirely different threat to American investors, companies and workers — one that cannot be solved by sanctions, military buildups in the Pacific and threats of retaliation.

China-bashing is not as simple as it used to be.

Republican candidates — led by Senator Marco Rubio of Florida, who on Friday described China as “a rising threat to our economic interests” and “a growing danger to our national security” — see a chance to cast President Obama as weak and untroubled by the possibility that a new power could gradually displace American influence. They see his lack of response to the theft of data of about 22 million Americans from the federal Office of Personnel Management, which government officials have concluded to have originated in China, as the latest evidence of that.

But if crafting a workable approach to China has been difficult for Mr. Obama, who once erupted in the Situation Room because he had no leverage to change Chinese behavior, it is as tricky for the candidates who wish to succeed him. It is one thing to describe the rising-power problem, and another to find a convincing approach to addressing it.