Donald Trump has demonstrated a worldview that could undo everything the United States has done to build its presence and influence around the world, especially in Asia, including the alliances with South Korea and Japan, a U.S. expert has warned.

Robert Manning, a senior Asia affairs expert at the think tank Atlantic Council, made the case in a recent article, refuting Trump's arguments one by one and warning that his election as president could "could unravel the entire post-World War II order."

"Most dramatically, Trump expressed a willingness to withdraw U.S. troops, rip up longstanding treaty alliances with Japan and South Korea, and have them obtain their own nuclear weapons," Manning said in the article posted on the think tank's website.

Trump has long argued that the U.S. has been defending wealthy nations like Japan, South Korea and Saudi Arabia in exchange for almost nothing and those countries should pay more for the protection. He also suggested arming South Korea and Japan with nuclear weapons as a way to reduce U.S. security burdens.

"Trump does not view the United States' overseas presence and alliance network as public goods that enable U.S. global leadership, deter adversaries and enforce a rules-based international system," Manning said.

"For Trump, it seems a matter of 'protection money.' Never mind the shredding of U.S. nuclear nonproliferation policy that, with a few notable exceptions, has fostered a norm against the spread of fissile material and nuclear weapons," he said.

The expert pointed out Trump's ignorance of the fact that Japan and South Korea have long shouldered sizable amounts of the costs necessary for the upkeep of American troops stationed in the two countries -- 50,000 troops in Japan and 28,500 in South Korea.

"In any case, without a forward-based air and naval force, the United States would not be able to project force across the region and quickly ebb as a Pacific power," he said. "The U.S. nuclear umbrella and extended deterrence in Asia has underpinned peace and unprecedented prosperity in Asia."

U.S. trade with Asia exceeds $1.6 billion annually, including some $600 billion in exports of goods and services, he added.

The expert also said that Trump has chosen "a peculiarly odd time" to raise the specter of U.S. withdrawal and nuclearization of Northeast Asia, saying North Korea is working feverishly to build intercontinental ballistic missile capability and nuclear weapons, and China is growing assertive in its maritime claims.

"Since World War II, U.S. global leadership has underpinned security and economic prosperity in Europe and Asia. In the Asia-Pacific, the U.S. military presence, the power of the U.S. market and the appeal of the values of an open, rules-based system has helped the region become an engine of unprecedented economic growth," he said.

"But Donald Trump appears ready to change all that," he added.

U.S. President Barack Obama has also openly criticized Trump for suggesting nuclear armament for South Korea and Japan, saying the statements "tell us that the person who made the statements doesn't know much about foreign policy or nuclear policy or the Korean Peninsula or the world generally."

Speaking at a news conference at the end of the Nuclear Security Summit, Obama also said the alliance with South Korea is one of the foundations and one of the cornerstones of the U.S. presence in the Asia-Pacific region and has underwritten the peace and prosperity of the region.

"It has been an enormous boom to American commerce and American influence. And it has prevented the possibilities of a nuclear escalation in conflict between countries that in the past and throughout history have been engaged in hugely destructive conflicts and controversies," he said.

"It is an investment that rests on the sacrifices that our men and women made back in World War II, when they were fighting throughout the Pacific. ... We don't want somebody in the Oval Office who doesn't recognize how important that is."  (Yonhap)