Changes appear inevitable to South Korea's defense cost-sharing agreement and free trade pact with the U.S. under a Donald Trump presidency as the businessman-turned-presidential candidate is determined to review the deals from scratch and overhaul them, if necessary, to maximize American interests.

Walid Phares, a top foreign policy adviser to the presumptive Republican presidential nominee, said in an interview with Yonhap News Agency and Yonhap News Television that Trump wants to "go back to ground zero" and is ready to renegotiate the landmark trade deal that has been in effect since 2012.

It was the first time that a Trump campaign official has mentioned the possibility of negotiating the pact that has been viewed as an economic alliance between the two countries. Renegotiation attempts could set off a diplomatic row.

"When we say renegotiate it does not mean cancel everything. It means to sit down and see, this is what has happened in America since the time we have negotiated and had the agreement and you tell us what are your cards, and we come closer," Phares said.

He also made clear that it's one of Trump's principles to have South Korea "share more" of the costs necessary for the upkeep of the some 28,500 American troops stationed in the country to help defend against North Korean threats.

"We'll see what the South Koreans can offer, or what the Japanese would offer, what our friends in the Middle East could offer. Then he would negotiate. He is good at negotiations," Phares said during the interview at his office in Washington.

Trump has long called for allies to pay more for U.S. defense support, claiming that the U.S. is protecting wealthy nations, such as South Korea, Japan and Saudi Arabia, in exchange for little. He has even called for Seoul to shoulder 100 percent of the costs, suggesting he could withdraw troops unless it agrees to pay more.

South Korea currently pays about half the costs, about US$900 million a year, to help finance the troop presence, and U.S. officials, including new U.S. Forces Korea Commander Vincent Brooks, said it would cost more to keep those troops stationed in the U.S. than it does in Korea.

Moreover, the American military presence on the peninsula is seen as in line with U.S. national interests in a region marked by an increasingly assertive China.

Phares cautioned against taking Trump's remarks as policy, saying they are still an expression of principles. He described Trump's call for Seoul to pay all costs for U.S. troop presence as a "maximum" position that a negotiator puts forward at the beginning of talks and evolves over time.

He also said that troop withdrawal from South Korea is "the last scenario to consider."

"Mr. Trump is not going to jump to the last scenario. This is the last scenario of crisis. But he is mentioning it to the American public that we really want to sit down and have a serious negotiation," he said, adding that Trump's mention of the scenario is "an expression of a negotiator," Phares said.

He also stressed that Trump's intention to review the cost-sharing agreement and the free trade deal do not mean at all that he's against the Asian ally.

"Mr. Donald Trump basically wants to be a president who would never abandon his allies on the one hand, and on the other hand, would confront those who are considered as national security threats to this country, but to our allies as well," Phares said.

"It is clear in the mind of Mr. Trump, and the mind of the people who elected him that the South Korean people have been standing with America for decades," he said, adding that the U.S. helped South Korea during the Korean War, and the South helped the U.S. in Vietnam, Afghanistan and elsewhere.

Phares summarized Trump's stance as "functionalist."

"In political science, functionalist means he wants to make sure that the interests of the U.S. first are taken care of and then theory of circles. Then our allies are taken care of. Then our partners are taken care of. Then the international security is taken care of," he said.

Trump's "America First" policy does not mean that he would ignore allies' interests, he said.

"He wants the national interest of the American people, first. ... It does not mean only. First does not mean only," Phares said.

"It means that for America to be able to continue with its international commitments, it needs to be strong." (Yonhap)