As North Korea advances its nuclear ambitions with yet another test of a long-range missile system, the once unthinkable has started to go mainstream in Japan: a discussion of the idea that Japan needs to have a nuclear deterrent of its own to survive in an increasingly unstable region.

Japan's "nuclear allergy" stems from its unique, tragic history with nuclear weapons. It is the only country in the world to suffer their impact, when the United States leveled Hiroshima and Nagasaki in 1945 to end World War II.

Since then, there have been brief public discussions of gaining nuclear weapons to stave off threats, such as in the '50s at the height of the Cold War, but such discussions were almost always relegated to extremists who longed for a return to Japan's imperial military heyday.

Today, experts tell Fox News the idea that Japan can and should possess nuclear weapons on its own soil, whether they are domestically developed or provided by the U.S., is no longer the exclusive realm of Japanese extremists.

"There are some Japanese security analysts who are starting to think about stationing nuclear weapons in Japan and they are mainstream. That is new in Japan," said Mark Fitzpatrick, Washington Executive Director of the International Institute for Strategic Studies and author of the book “Asia's Latent Nuclear Powers.”

"The taboo about talking about nuclear weapons in Japan has been broken," said Fitzpatrick.

"Although anti-nuclear weapons sentiment is extremely strong in Japan, now people are more freely discussing the idea of a nuclear-armed Japan," said Masako Toki of the Center for Non-proliferation Studies, "Before now, even slightly saying such an idea forced politicians to resign. Now that seems no longer the case. The taboo on discussing de-nuclearization has been weakened."

Children and residents conduct an evacuation drill on the assumption that North Korea may launch ballistic missile in Abu, Yamaguchi Prefecture on June 04, 2017 (AP Photo/Yomiuri)

Anders Corr, who runs a political risk consultancy called Corr Analytics, said he has also "seen an increased number of military analysts supporting a nuclear armed Japan over the past few months."

A combination of factors appears to be driving the new, albeit reluctant, discussion. They are: China's regional ambitions as a nuclear power, North Korea's testing where some missiles actually land in Japanese territorial waters, and a U.S. president who is seen as willing to test traditional alliances with a focus on domestic priorities.

As a non-proliferation advocate and analyst, Fitzpatrick does not support Japan gaining the bomb, but he is worried about what could happen as the region continues to destabilize, U.S. policy continues to evolve, and the idea that Japan must have nuclear weapons to protect itself gains ground.

"I think it's very dangerous talk because if it were to happen, it would exacerbate the regional arms race and enable the possibility of nuclear exchange, either intentional or accidental," Fitzpatrick told Fox News.

Public opinion polls still show large majorities against Japan nuclearizing and the barriers to the bomb are still very high, but "as China's aggression increases, political opinion in Japan will increasingly support going nuclear," Corr told Fox News.

Corr believes nuclear weapons would actually stabilize the region. Such weapons, Corr said, would have a deterrent effect on China, for example, from taking territory in and around the Senkaku Islands.

Japanese nuclear weapons also would deter Russia, which has taken "increasingly aggressive actions in Japan's airspace in recent years," not to mention North Korea, he said.

And they could neutralize the North Korean menace.

"It would restore some balance in East Asian Security. It would be a form of retaliation that does not escalate, but actually de-escalates tensions in East Asia," Corr added.

Non-proliferation experts disagree, and argue that a nuclear-armed Japan would create immense diplomatic problems for the United States as it continues to try to prevent proliferation by adversaries and allies alike.

Plus, Japan is already defended by nuclear weapons. "They're just not Japanese nuclear weapons. They're American nuclear weapons," said James Acton, Co-Director of the Nuclear Policy Program at the Carnegie Endowment for International Peace. "This is crucial to the argument against Japan going nuclear."

Japan's government of Prime Minister Shinzo Abe surprised observers last year when it seemed to lean toward interpreting the country's pacifist Constitution, as permitting some kinds of nuclear weapons. However, it has made seemingly contradictory statements on the matter.

Yusuke Yokobatake, the Director-General of the Japanese Cabinet Legislation Bureau, said in March 2016, "We don't think that the use of all kinds of nuclear weapons is prohibited under the Constitution . . . [but] the use of weapons, not just nuclear arms, is restricted under domestic and international laws."

Abe's political party also has stated that North Korea's political threats have "entered a new stage." Without referencing nuclear weapons, Japan's prime minister said earlier this year that the country needs to explore "what kind of deterrents can be possible under the exclusively defensive policy."

Thanks to its reliance on nuclear power, Japan has a large stockpile of plutonium that has long worried anti-proliferation advocates.

As of the end of 2016, Japan had 9.8 metric tons of plutonium stockpiled around the country and another 37.1 metric tons stored in Britain and France. That's enough to create around 5,000 nuclear bombs. Some of the weapons-grade material was transferred to the US in March under an anti-proliferation agreement signed during the Obama Administration.

After North Korea successfully tested an Intercontinental Ballistic Missile capable of carrying a nuclear warhead over the weekend, President Trump reassured Abe that the U.S. remains committed to using the "full range" of its capabilities in defending Japan.

But Acton said that allies like Japan and South Korea are nevertheless worried about the Trump administration's dedication to so-called extended deterrence, or the protective shield of the American nuclear umbrella over allies, not just the U.S. homeland.

"One gets into a problem where allies no longer trust that guarantee," Acton told Fox News.

While the Trump Administration has not given any indication that Japan or South Korea should get nuclear weapons, Acton said they do have lingering concerns given the president's statements on issues like paying for protection, such as Trump's call on South Korea to pay more for the THAAD missile defense system.

"That kind of event gives allies concerns about whether the U.S. is actually committed to their security," Acton said.

During the presidential campaign, Trump was criticized for apparently leaning toward a nuclear-armed Japan when he said at a town hall, "you have so many countries now that have them already - China, Pakistan, Russia. Now, wouldn't you rather in a certain sense have Japan have nuclear weapons when North Korea has nuclear weapons?"

Trump later distanced himself from the prospect of supporting a nuclear-armed Japan.

But Corr, who believes Japan would be wise to nuclearize, points out that Trump is on to something when it comes to adversaries gaining the bomb, and allies leaning heavily on America for protection.

"The democracies and U.S.-aligned countries are playing by the rules," he said, "it would be unwise to let all the autocracies and China-aligned countries obtain nuclear weapons, and deny that deterrent to our democratic allies."

He argues that time has come in East Asia.

"Not only Japan, but South Korea and Taiwan should obtain independent deterrent nuclear forces," said Corr. "This would right the current security imbalance in East Asia and decrease incentives for Chinese and North Korean territorial aggression."

Fox News Researcher Joseph LoGalbo contributed to this report.