Just days before his much-awaited White House memoir hit the shelves, former U.S. National Security Adviser John Bolton said in a TV interview that he hopes to provide the "basic evidence" that will help the public know what they would actually be voting for if they choose incumbent Republican President Donald Trump in the November election.

In terms of the U.S.-Japan relationship, possible repercussions of a second Trump term may include a standoff over the costs of stationing U.S. military troops in Japan that could overshadow the decades-old alliance, experts say.

U.S. National Security Adviser John Bolton is pictured at Japan's Foreign Ministry in Tokyo on July 22, 2019. (Kyodo) 

The 592-page book "The Room Where It Happened" went on sale Tuesday as scheduled, even as the Trump administration has scrambled to block its publication, claiming that it contained classified information to which Bolton gained access while serving as a high-level adviser for more than a year before being sacked by the president in September 2019.

It is no secret that Trump has been vocal about the need for allies to pay their "fair share" for U.S. security support or else defend themselves, an argument he has made including during his 2016 presidential campaign.

But the memoir offers a close-up look at his approach to alliances based on his cost-benefit calculations, underscoring two issues on which some experts say the 74-year-old businessman-turned-president is "uniquely stubborn" -- so-called host-nation support and trade imbalances.

James Schoff, an expert on Japan-U.S. relations at the Carnegie Endowment for International Peace, said he believes Trump, to some extent, has come to appreciate the value of the friendship with Japan, which "never creates the same kind of drama at multilateral forums" that sometimes happens with Germany and other countries.

"But he can't get over those two big things, the trade deficit and the burden-sharing piece," he said, adding, "So that constantly interrupts or disturbs what is otherwise a pretty smooth-functioning alliance relationship."

In the memoir, Bolton wrote that Trump, despite "countless discussions," thought allies were not paying enough and the U.S. troops stationed in countries like Japan and South Korea are there to defend the Asian countries, in which the United States had no particular interest.

U.S. President Donald Trump walks out of the White House to make a statement to the press about restoring "law and order" on June 1, 2020 in Washington, DC. (PHOTO NOT FOR SALE)(Getty/Kyodo)

"We were not there for 'collective defense' or 'mutual security' or any of that complex international stuff," Bolton said as he explained Trump's standpoint. "Moreover, as any good businessperson would tell you, we should make a profit from defending all these countries."

Trump at least wanted to start negotiations on host-nation support with "cost plus 50 percent," a phrase which he was persuaded to obliquely call a "fair share" because the former term sounded "too raw."

During his trip to Japan in July 2019, Bolton conveyed Trump's request that Japan pay $8 billion annually, more than four times the current amount Tokyo shoulders.

When Bolton returned to Washington and briefed Trump, the president said, while also referring to a demand for $5 billion in host-nation support from South Korea, that "the way to get the $8 and $5 billion annual payments, respectively, was to threaten to withdraw all U.S. forces."

Japan's top government officials have denied that the U.S. side urged Tokyo to pay much higher costs for the U.S. military, with Defense Minister Taro Kono saying that negotiations have not "even started."

Japanese Prime Minister Shinzo Abe (L) and U.S. President Donald Trump shake hands in New York on Sept. 25, 2019, after reaching a bilateral trade agreement during their talks. (Kyodo) 

Schoff said the pullout of U.S. troops may be "an empty threat" as it would be logistically difficult and costly to do so given the types of military assets deployed in Japan. But he warned that Trump's approach could be "a huge thorn" in the alliance, and eventually would create an "irritation" that begins to overwhelm some of the better-functioning aspects of the relationship.

The cost-sharing negotiations have, according to Bolton, "bedeviled relations" with South Korea. Washington and Seoul have not been able to reach a new deal after the previous agreement expired at the end of last year.

Japan and the United States are expected to start negotiations on host-nation support later this year, given that the current five-year payment agreement is set to expire at the end of next March. Japan's financial support totals nearly 200 billion yen ($1.9 billion) annually, covering costs for base workers, utilities and other items.

In 2017, then U.S. Defense Secretary Jim Mattis said Japan's cost-sharing burden for hosting U.S. forces is "a model" for other nations to follow. As of fiscal 2015, Japan was shouldering 86.4 percent of the cost, according to Japanese Defense Ministry calculations.

Tokyo has also maintained that the Japan-U.S. alliance is a mechanism that provides benefits to both countries.

Under the Japan-U.S. security treaty, about 50,000 U.S. troops are stationed in Japan, enabling the United States to respond rapidly to contingencies in the Asia-Pacific region. The U.S. 7th Fleet -- the U.S. Navy's largest forward-deployed fleet whose area of responsibility stretches from the Western Pacific to the Indian Oceans -- is based in Yokosuka, south of Tokyo.

The Blue Ridge, the U.S. 7th Fleet's command ship, is pictured in Hong Kong on April 20, 2019. (Kyodo)

While a one-term Trump presidency has not been a "terribly damaging thing to the alliance," a second term could have a different meaning than when he was first elected in 2017 after starting off his campaign as a political outsider and an underdog candidate, Schoff said.

"It was easy enough for a lot of Americans to, even if they didn't completely buy into the 'America First' rhetoric or other things, they thought 'Well, Trump's a businessman, you know, other people will be around him.' And that he'll be moderated and it won't be so disruptive. That's clearly not the case," said the senior fellow at the Washington-based think tank.

"I think, if the American voter re-elects Trump in a one-on-one with (Democratic presumptive nominee) Joe Biden...Japan's calculations change to some extent -- that this is not just a Trump phenomenon, this is a broader U.S. political phenomenon that has potentially longer lasting implications for Japan's strategy in security," he said.