For decades, U.S. scholar Harry Harding has filtered the academic literature on Sino-U.S. relations. Today, the University of Virginia professor sees hardening positions in Beijing and Washington, as well as on Main Street U.S.A. and from a current perch as a visiting professor at the Hong Kong University of Science and Technology.

While he predicts China and the U.S. can avoid conflict, Mr. Harding worries a new kind of Cold War may limit the ability of the two governments to cooperate, or lead to bad accidents. Nationalism could rise in China as its economy weakens, he says. Washington’s support for Taiwan is growing, along with pessimism about China’s president.

Whoever next occupies the White House may need to reset the relationship. “The United States is now immersed in its most intense debate over China policy in decades—certainly since the Tiananmen Crisis of 1989, and possibly since the first serious discussion of normalizing relations with China in the mid-1960s ,” he wrote in a paper last year.

The Wall Street Journal’s James T. Areddy met Mr. Harding this week in Shanghai. The following is an edited version of the interview.

WSJ: What is the new mainstream in the U.S. on China?

Mr. Harding: I think there is a consensus on the fact that (Washington’s China) policy has had disappointing results, or that China’s behavior has been deeply disappointing both at home and abroad. The center of gravity is, stay the course but try to be smarter. Have a better balance and better implementation of the elements of current policy,with probably a little more emphasis on balancing than on simply engagement.

There would be less emphasis on integrating China into an international order. That’s already happened and the results have been mixed. What we are seeing in much of the debate now is, “We have to get our act together at home.” What kind of example is the United States setting in terms of economic success, a well-functioning democratic system?

I think this is another emerging part of the new mainstream: we are in a competitive relationship with China. In fact, we want to have rules that preserve competition.

WSJ: How has the debate in the U.S. changed?

Mr. Harding: (As former U.S. President Richard Nixon put it,) What brought us together was a common threat from the Soviet Union; what will keep us together is economics. That is a theme that optimists about China regularly quote.

This theme that economic interdependence will prevent things from spinning out of control … there’s a large element of truth to it, but I think increasingly the world is questioning the issues of the costs and benefits of globalization.

WSJ: Who is driving the debate?

Mr. Harding: Overall, the plurality of Americans see China as a friend, not an ally. They see it mainly as an economic problem. This is not a public that is angry about China. China is an example of the threats that globalization is posing to the American way of life. This is (presidential candidate Donald) Trump’s appeal. They would like someone who can do something about it.

WSJ: Do you believe in the Thucydides trap, that a rising power is predestined to clash with the incumbent power? (The term for an inevitable war between rival states takes its name from an ancient Greek historian whose analysis described how rising Athens was always going to challenge superpower of the day, Sparta.)

Mr. Harding: We are in another situation of mutually assured destruction. … We avoided war against the Soviet Union because of mutual deterrents. We should be able to avoid war with the Chinese. But that competition could be costly – accidents, incidents. We’ve really got to work on crisis management (and) mutual security reassurances. I don’t think the Thucydides trap is going to be a trap snapping on the two parties. But this is becoming a more competitive relationship.

WSJ: And how will the rivals compete?

Mr. Harding: The issue is not actually conflict. … The equally serious threat is the inability to cooperate. There are issues now where China and the U.S. need to be able to cooperate.

And if they are in a highly competitive and mistrustful relationship, that makes cooperation much more difficult because there’s going to be enormous suspicion. When the Chinese talk about stability on the Korean peninsula they define the word very differently. I thought it meant no war. They meant it as no regime collapse.

Just having dialogue doesn’t really do it. What you really need are concrete measures where one party gains trust by actually paying a price. Costly reassurance.

WSJ: How does China’s weakening economy change dynamics?

Mr. Harding: It’s interesting that so much of the debate on China policy was assuming an inexorably rising China.One school of thought was we need to counterbalance China. Another school of thought said we need to accommodate China because we have the upper hand now but won’t in the future. Now, suddenly you have the sense that China may be in fairly serious difficulty domestically.

I am worried about this and the ease with which China is blaming problems on external influence. The problem with that, of course, (is) okay, you blame the foreigners – but then your mobilized public is going to say, “What are you going to do about it?” If China gets into deeper difficulty at home, yes, the common external threat is a very tempting way to try to maintain internal order. More the Chinese style: react very strongly to any trigger, that the foreigners are doing something that violates China’s interests, as opposed to doing something more assertive.

WSJ: What have you learned while in Hong Kong?

Mr. Harding: It relates to these liberal myths about dialogue and exchange: “To know them is to not necessarily to love them.” In Taiwan, (people are saying regarding China), “We don’t want to be like them.” In Hong Kong, the phrase is now “mainlandization.” It’s not a positive development.

I think there is going to be somewhat greater sympathy for Taiwan in the United States. I think there’s going to be sympathy for Hong Kong in the United States.

WSJ: Chinese say they prefer a strong leader. Do Americans want a strong Chinese leader?

Mr. Harding: It clearly depends on what the strong leader does. There are still some people I talk to who have hopes for Xi Jinping — that when he gets his power consolidated and when corruption is under control and the economy is back on track, he will engage in political reform. I see no evidence of that. In this particular case, it’s a small and declining number of people.

WSJ: How should U.S. policy toward China change?

Mr. Harding: It’s going to be a bargaining relationship, and we are going to have to put some chips on the table selectively. We do need to work with China in dealing with a wide range of newly emerging issues. The focus really has to be not only on the Thucydides trap and these traditional issues. There are so many new issues that the old formulas don’t cover.

It’s a conceptual Thucydides trap. The security aspects of it – that’s the classic trap. It’s the mutual suspicion and the inability to cooperate that I think is the real problem. It is a Thucydides trap for the 21st century.

 –James T. Areddy.