Republican presidential candidate Donald Trump is dealing with friends and allies with a tactic best suited to bargaining with enemies, a renowned U.S. foreign policy scholar said.

Harvard University professor Joseph Nye, considered a key Asia policy adviser to Democratic presidential candidate Hillary Clinton, made the point in a recent article contributed to the Project Syndicate, expressing concern that Trump is taking a "disastrous approach" to allies.

"Weakening America's alliances, the likely result of Trump's policies, is hardly the way to 'make America great again.' America will face an increasing number of new transnational issues that require it to exercise power with others as much as over others," Nye said.

Nye, creator of the popular "soft power" concept of preferring persuasion over force, pointed out that the real-estate mogul "extols the virtues of unpredictability -- a potentially useful tactic when bargaining with enemies, but a disastrous approach to reassuring friends."

Trump has unnerved foreign countries, especially such allies as South Korea and Japan, as he has displayed deeply negative views of U.S. security commitments overseas, contending the U.S. should stop being the policeman of the world.

Trump has said that the U.S. should be prepared to end protection of allies unless they pay more. He even suggested allowing South Korea and Japan to develop their own nuclear weapons for self-defense so as to reduce U.S. security burdens.

"Alliances not only reinforce US power. They also maintain geopolitical stability, for example, by slowing the dangerous proliferation of nuclear weapons. While U.S. presidents and defense secretaries have sometimes complained about its allies' low levels of defense spending, they have always understood that alliances are best viewed as stabilizing commitments like friendships, not real-estate transactions," Nye said.

What sets the U.S. apart from the dominant great powers of the past is that "American power is based on alliances rather than colonies," the professor said, citing British strategist Lawrence Freedman.

"Contrary to claims that the 'Chinese century' is at hand, we have not entered a post-American world. The U.S. remains central to the workings of the global balance of power, and to the provision of global public goods," the professor said.

"But American preeminence in military, economic, and soft-power terms will not look like it once did ... More than ever, America's ability to sustain the credibility of its alliances as well as establish new networks will be central to its global success," he said. (Yonhap)