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Senator Marco Rubio of Florida at an event in South Carolina on Friday.Credit Sean Rayford for The New York Times

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 cyberattacks 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.

Most have not tried. Gov. Scott Walker of Wisconsin recently called for the cancellation of next month’s state visit by President Xi Jingping. But in 2013, he did what most governors do: He traveled to China, promoted Wisconsin products there, hailed the importance of the Chinese market for American firms and had his photo taken with Chinese leaders. Former Gov. Rick Perry of Texas was there last September advertising his state as a business-friendly climate for Chinese investors.

Donald Trump Jr., the candidate’s son, has been put in charge of new investments for the Trump hotel empire, including, according to the group’s website, deals in mainland China. When his father suggested the other day that the state dinner for Mr. Xi should be replaced by a McDonald’s hamburger, the Chinese must have been tempted to point out that they need no introduction to such American fare. There are more than 2,000 McDonald’s in China, including some a very short walk from Mr. Xi’s official residence.

In a speech in South Carolina on Friday, Mr. Rubio presented a familiar list of grievances with Mr. Xi’s government: a “campaign to push America out of Asia”; the development of “weapons that threaten our bases and naval assets” (the Chinese say the same about the United States.); and an effort “to make the 21st century a Chinese Century” (though American politicians have no compunctions about calling it an “American Century”).

He talked at length about Chinese efforts to round up human rights activists, oppress Christians, detain dissidents and control the Internet. “This is a disgrace,” he concluded. “And we must stand against it.”

But his problem was also familiar: As Hillary Rodham Clinton put it early in her time as secretary of state, in a confidential conversation later published by WikiLeaks, “How do you talk toughly to your banker?”

Mr. Rubio struggled with answers. He said engagement, yet his solutions sounded a bit like Mr. Obama’s. He called for ending sequestration on the Pentagon budget so more planes and ships could be devoted to Asia. Specifically he promised to build two Virginia-class submarines per year, deploy “new long-range precision strike systems,” deploy more missile defenses and protect satellites and other space-based systems from Chinese attack. He will find many of those in the current Pentagon long-range plan.

Mr. Rubio stepped carefully when it came to calling for “aggressive retaliation, which would hurt us as much as them.” Instead he said the United States should reinforce “our insistence on free markets and free trade. This means immediately moving forward with the Trans-Pacific Partnership and other trade agreements that strengthen strategic ties with our partners in Asia.” Mr. Obama would argue that is exactly what he is attempting.

Mr. Rubio seemed to sense the dilemma of figuring out whether a strong China or a weak one is the harder problem for the next decade.

“We tend to exaggerate their capacities in both directions,” said Kurt M. Campbell, who served as assistant secretary of state for East Asia under Mrs. Clinton and who still advises her on Asia and foreign policy. “There was the 10-foot-tall-ism, where we focused too much on their strengths,” said Mr. Campbell, who now runs the Asia Group, a consultancy. “Now we have to avoid spending too much time on their weaknesses.”

Rightly or wrongly, Mrs. Clinton is considered to be more confrontational with the Chinese than Mr. Obama, after a famous flare-up with her Chinese counterpart over the country’s territorial claims.

As a result, the Republicans know that if Mrs. Clinton emerges as the Democratic nominee, it will be difficult to cast her as soft on China. A bigger problem may be in their own party. The American opening to China was a Republican president’s project. It is considered one of the greatest accomplishments of Richard M. Nixon’s checkered presidency, and today’s mainline Republican foreign policy establishment takes a very nuanced view of balancing Chinese power.

Whoever emerges from the scrum of 17 Republican candidates will seek the wisdom — and the endorsement — of Henry A. Kissinger, Mr. Nixon’s national security adviser and secretary of state, and at 92 still the party’s greatest foreign policy mind. The architect of the American relationship with Beijing, who four years ago published a book on America’s dealings with China, is not one to call for cutting off relationships with Beijing.

Neither is former President George W. Bush. Shortly after the Sept. 11 attacks, he traveled to Beijing and got the Chinese to support his counterterrorism agenda — which the Chinese immediately exploited as a justification for crackdowns on the ethnic Uighur population, which is largely Muslim. But Mr. Bush viewed the visits of Chinese leaders to his Texas ranch as critical to his effort to contain North Korea, and always described the relationship between China and the United States as “complicated.”

It is a tricky moment for the Obama administration as well. Mr. Obama’s national security adviser, Susan E. Rice, is in Beijing to meet Mr. Xi and sort through the agenda for his state visit to Washington next month. Ms. Rice’s agenda is to figure out how to find common ground — on the Iran nuclear agreement, climate change and renewed threats from North Korea — while not appearing to back down on the territorial claims or the cyberattacks on the United States from China.

The dynamic will become more complicated when Mr. Xi arrives in the United States. Battered by an economic crisis he did not see coming, Mr. Xi “is likely to want to show he is not vulnerable, and not weak,” Mr. Campbell said.

“He comes to Washington wanting respect, and I do not believe we will see particular lines of easing on maritime issues and cyberintrusions,” he added. But with global economic stability at stake, Mr. Obama and Mr. Xi have a strong interest in demonstrating to the markets that they can work together and ignore the din of a campaign.