Trump shock spurs Japan to think about the unthinkable: nuclear arms

Matsukawa, a former deputy defense minister, traveled in March to historic Fordham Abbey for a top-level bilateral conference. At the estate, now home to a Japanese-owned sake brewery, she said she learned from British lawmakers, diplomats and business leaders that a tectonic shift in their thinking was underway.

U.S. President Donald Trump was openly berating America’s European allies and tilting toward Russia. And Europe had “awakened,” she said, to the fact it could no longer rely so heavily on America and must take more responsibility for its security.

This was also true for Japan, currently the home to the largest overseas contingent of U.S. troops globally, she realized. “You can’t really take the U.S. presence for granted,” said Matsukawa, a member of the ruling Liberal Democratic Party’s (LDP) influential national security policy council.

Matsukawa is part of a contingent of senior Japanese lawmakers who are beginning to think the unthinkable in the only nation to have suffered an atomic bomb attack: Surrounded by nuclear-armed neighbours China, North Korea and Russia, Japan too might have to deploy those weapons of mass destruction.

“Trump is so unpredictable, which is his strength maybe, but I think we have to always think about Plan B,” Matsukawa said in an interview at her Tokyo office. “Plan B is maybe go independent, and then go nukes,” she added, raising the possibility of Japan reducing its reliance on American security guarantees.

The Trump shock is also reverberating in neighbouring South Korea, currently protected under the U.S. nuclear umbrella like Japan. Up to 75% of the South Korean public is in favor of the country building its own nuclear weapons, polling shows. The election of left-center President Lee Jae Myung in June has dampened some of the more overt talk of nuclear weapons in Seoul. But even some in his Democratic Party are increasingly recognizing the need, should U.S. security commitments falter, to achieve “nuclear latency” – possessing the means to quickly build a usable atomic arsenal.

Support in Japan for developing its own indigenous atomic weapons is smaller. Matsukawa, for instance, stresses that the U.S. remains an important ally and says Tokyo needs to persuade the Trump administration that it is in America’s interest to defend her country and deter a crisis over Taiwan.

But interviews with a dozen Japanese lawmakers, government officials and former senior military figures reveal there is a growing willingness to loosen Japan’s decades-old pledge, formulated in 1967, not to produce, possess or host nuclear weapons in its territory – what is known as the “Three Non-Nuclear Principles.”

Among the Japanese public, too, opinion surveys show a greater readiness to rethink the nuclear stance. Hiroshima native Tatsuaki Takahashi, whose grandfather survived the atomic bomb attack on the city, told Reuters that views on the issue are changing as the tragedy of the past becomes more distant.

The shifting attitudes in Japan and South Korea, both key pillars of America’s decades of dominance in the Pacific, have been spurred by a growing loss of faith among U.S. allies in Washington’s commitment to their security, in particular doubts about whether America will come to their aid in a conflict.

Trump’s election on an America-First platform and his spurning of America’s traditional allies has turbo-charged these concerns, interviews with lawmakers and officials in Japan and South Korea show. The president’s sowing of doubt about continued U.S. support for NATO, imposition of tariffs on Japan, South Korea and Australia, and talk of absorbing Canada into the U.S., have spooked many of America’s long-time allies.

The White House did not respond to a request for comment, but a senior Trump administration official told Reuters that there are “no changes in U.S. policy” toward Japan and South Korea. Trump and his senior national security aides have repeatedly stressed their commitment to allies in Asia.

Japan’s foreign ministry said the government considers the Trump administration’s commitment to the bilateral alliance “to be unwavering.” The defense ministry said Japan has “full trust in the U.S. fulfilling its obligations using all types of capabilities, including nuclear forces.”

South Korea’s foreign ministry said its decades-old alliance with the U.S. remains “the foundation of our diplomacy and has played a key role in maintaining peace and stability on the Korean Peninsula.”

China’s defense ministry said it opposed “any attempt to hype up the so-called ‘Chinese nuclear threat’ in an effort to smear and defame China and deliberately mislead the international community.” China, the ministry added, continues to adhere to a no-first-use policy – “not to use or threaten to use nuclear weapons against non-nuclear-weapon states or nuclear-weapon-free zones.”

RETHINKING THE NUCLEAR UMBRELLA

For Tokyo, which in recent years has taken historic steps away from its post-war pacifism to rebuild its military capabilities, the nuclear question is the final security taboo.

Eighty years ago this month, Hiroshima and Nagasaki were devastated by atomic bombs at the end of World War Two. Japan renounced war and vowed never to possess the military means to attack other countries. It also became a vocal proponent of nuclear disarmament.

Prime Minister Eisaku Sato, who formulated the Three Non-Nuclear Principles, won the Nobel Peace Prize in 1974 for this policy achievement and for signing the Treaty on the Non-Proliferation of Nuclear Weapons. Last year, Nihon Hidankyo, an organization established by survivors of the atomic bomb attacks, also won the prize.

Until now, Japan has relied on U.S. nuclear weapons, which once laid waste to Nagasaki and Hiroshima, to deter modern-day threats. In a security arrangement called “extended deterrence,” Washington has committed to use the full range of its military capabilities, including nuclear, to defend Japan and other allies.

In recent years, however, Tokyo has begun to adopt a more robust stance in its bi-annual closed-door talks on this arrangement with the U.S., Reuters has learned. Tokyo has been delving into subjects such as how its conventional military could practically support U.S. nuclear forces in a conflict, two former U.S. officials with direct knowledge of the talks said.

This has included discussions on how Japan's ongoing efforts to acquire new, longer range “counter-strike” missiles could allow it to take out enemy launch platforms to deter or assist in a nuclear conflict, said the two officials. They spoke on condition of anonymity due to the sensitivity of the talks.

The two sides have also explored how Japan's surveillance and intelligence apparatus could support the U.S. nuclear mission and chalked out a roadmap for how the two governments and militaries would coordinate in a nuclear emergency, the former officials added. These details have not been previously reported.

Japan’s foreign ministry declined to comment on the details of the talks. The defense ministry said Japan and the U.S. “have been working to strengthen extended deterrence,” but declined to comment further. The State Department said America’s “extended deterrence commitments” to Japan and South Korea “are ironclad.”

Now, lawmakers from Japan’s ruling Liberal Democratic Party are considering how they can reinforce the credibility of the nuclear umbrella, according to interviews with Matsukawa and four other senior party members. They suggested that the non-nuclear principles could be revised or reinterpreted to allow U.S. nuclear weapons to enter Japanese territory, noting that the principles are not set down in legislation or legally binding. Matsukawa said the widely publicised visit of a U.S. submarine designed to carry nuclear weapons to South Korea in July 2023 provided an example Japan could follow to bolster deterrence.

Matsukawa and three former senior military commanders said Tokyo should also prepare for the possibility of nuclear sharing, a concept that allows non-nuclear states to participate with its nuclear-armed allies in planning, training and use of nuclear weapons.

Belgium, Germany, Italy, the Netherlands and Turkey, for instance, have been hosting U.S. nuclear weapons on their soil as part of NATO’s nuclear-sharing strategy. In the event of a nuclear war, these non-nuclear states could deliver those weapons to targets on behalf of the U.S., using their own aircraft. Before taking office, Japanese Prime Minister Shigeru Ishiba advocated for an Asian version of NATO that could include nuclear sharing.

Japan “has no intention” of revising its non-nuclear principles, the Liberal Democratic Party said in response to questions. But Ishiba has instructed the party “to examine Japan’s future security arrangements in Asia,” it said.

The foreign ministry said the government “does not consider nuclear sharing to be permissible.” Japan, it said, “will not possess nuclear weapons.” Ishiba’s office said the foreign ministry’s responses represented its views.

CONFIDENCE SHAKEN

Doubts about the reliability of American security guarantees didn’t start with Trump.

When the Obama administration didn’t respond to Chinese island-building and reclamation in disputed territories of the South China Sea, starting in 2013, it raised questions about Washington’s stomach for confrontation with Beijing, said Taro Kono, a ruling party lawmaker who previously served as foreign and defense minister.

After Russia invaded Ukraine, President Joe Biden sent tens of billions of dollars in military aid to Kyiv. But Biden also said the U.S. wouldn’t fight World War Three over Ukraine.

The Biden administration’s Ukraine policy rattled political and military strategists in Tokyo and Seoul. Russia has repeatedly threatened to use nuclear weapons to limit outside intervention in the war. The apparent success of that nuclear intimidation has fueled anxiety over the readiness of the U.S. to protect its allies, said Tomohisa Takei, a retired admiral who helmed Japan’s navy from 2014 to 2016.

“Out of concern for escalation, the United States became cautious even about the types and capabilities of weapons it provided to Ukraine,” Takei said. “I believe that the credibility of extended deterrence has been significantly shaken for countries under the U.S. nuclear umbrella.”

Song Seong-jong, a retired South Korean military officer, said Ukraine’s fate after earlier giving up its nuclear weapons served as a warning. “Do you think Trump will retaliate with nuclear weapons for the sake of South Korea?” he said, referring to a potential conflict with North Korea.

Song doesn’t think Trump would. “This is an inconvenient truth,” he said.

Trump and top administration officials have repeatedly stated in public that the U.S. is committed to remaining a Pacific power. In meetings last month with the Japanese and South Korean foreign ministers, Secretary of State Marco Rubio discussed enhancing security cooperation, according to State Department statements.

Adding to the anxiety in Asia has been Beijing’s rapid expansion of its nuclear arsenal, a decisive break with China’s earlier preference for a small force sufficient to maintain deterrence. North Korea’s fielding of increasingly sophisticated ballistic nuclear missiles has also heightened concern.

China has the fastest-growing nuclear arsenal globally, adding about 100 new warheads per year since 2023, the Stockholm International Peace Research Institute said in its annual inventory of the world’s most dangerous weapons published in June. China has some 600 nuclear warheads, while the U.S. and Russia have stockpiles of 3,700 and 4,309 warheads respectively, according to estimates by the research institute.

In 2016, before the presidential election, Trump suggested Japan and South Korea might need nuclear weapons because of the threat posed by North Korea and China. Actions he has taken at the start of his second term have made some in Asia think he was right.

Since his re-election, Trump and senior members of his administration have raised questions about America’s commitment to NATO, with the president saying the U.S. wouldn’t defend member countries unless they increase defense spending.

Trump’s trade war, which targets even U.S. allies, has further eroded faith in American commitment to long-time friends. After threatening to impose tariffs of 25% on Japan and South Korea, Trump last month reached deals with Tokyo and Seoul that put a 15% tax on imports from both countries.

“Trump’s tariffs hit allies the hardest,” said Itsunori Onodera, a former defense minister and currently the ruling party’s policy chief. “The tariffs risk pushing them closer to China, the very countries the U.S. should be aligning with” to counter Beijing.

Ryoichi Oriki, who served as chief of staff of the Joint Staff of Japan’s Self-Defense Forces from 2009 to 2012, said the American president’s “volatility on trade” has created doubts about U.S. security commitments. “The U.S. has become a variable, not a constant, which affects trust,” he said.

In South Korea, former President Yoon Suk Yeol raised the prospect in early 2023 that Seoul could be forced to pursue nuclear weapons in the face of a mounting threat from North Korea. He backed off later that year when Seoul extracted extra security assurances from the Biden administration with the signing of the Washington Declaration. That pact included giving South Korea greater insight into U.S. nuclear planning for any conflict with North Korea.

Yoon was impeached after plunging the country into crisis when he declared martial law in December last year. While newly elected President Lee Jae Myung has rejected the idea of nuclear armament, his intelligence agency chief, Lee Jong-seok, this year called for Seoul to secure the right to enrich uranium to demonstrate its “potential nuclear capabilities.”

It would be a mistake to “interpret South Korean nuclear ambitions as a bluff,” says Ely Ratner, who served as assistant secretary of defense for Indo-Pacific security affairs in the Biden administration.

South Korea’s foreign ministry said the government isn’t considering the acquisition of nuclear weapons.

CHANGING ATTITUDES

There is broad public support for acquiring nuclear weapons in South Korea, in the face of threats from nuclear-armed Pyongyang. In Japan, public opinion is constrained by the weight of its history – though attitudes are changing.

A poll in March found that 41% of respondents were in favor of revising Japan's Three Non-Nuclear Principles. In a similar poll three years ago by the Kioicho Strategy Institute, a consultancy and think tank, just 20% backed the idea.

Even some Japanese with personal connections to the atomic attacks are calling for a shift on the bomb.

Tatsuaki Takahashi, the Hiroshima native, said his grandfather was just four years old when the bomb was dropped on the city at 8.15 am on August 6, 1945, but could still vividly recall the flash-and-boom and the windows in his home shattering. Some of Takahashi’s relatives went missing during the disaster and were presumed to have died, he said.

Growing up in Hiroshima, Takahashi believed that diplomacy and dialogue could help avert a repeat of that nuclear nightmare. Now 28, and living as an IT programmer in Tokyo, he thinks Japan may need a show of nuclear strength to achieve that goal.

“Personally, I think allowing U.S. nuclear weapons into Japan might be unavoidable as a form of deterrence,” said Takahashi, who runs a group called Youth Vote Hiroshima, which aims to engage young people in his home city in politics through social media. “I’m still against using nuclear weapons, but just possessing them has strategic value.”

Takahashi said Japanese views on the issue are changing as the memory of the bombings dims and younger people think more critically about the need for deterrence.

There are signs that even in Hiroshima, where the 80th anniversary of the attack was commemorated earlier this month, some people are increasingly reluctant to dwell on the past.

A survey published in April by public broadcaster NHK found more than 30% of people aged between 18 and 24 in the city and surrounding prefecture who had not heard the accounts of the city’s atomic bomb survivors said that they did not wish to do so. That was more than 6 points higher than a similar survey five years ago and higher than a 25% figure for the rest of Japan. The most common reason given was that the accounts were too horrific.

THRESHOLD STATE

Both Japan and South Korea have committed not to develop or acquire nuclear weapons by signing the NPT.

But security experts describe Japan as a threshold nuclear-weapons state – meaning it has the technical capacity, and could obtain the materials, to build and launch a bomb if it was determined to do so.

Within a couple of years, Tokyo could build a nuclear device small enough to fit on a missile, said Jennifer Kavanagh, director of military analysis at Defense Priorities, a Washington-based think tank. One senior lawmaker close to Ishiba told Reuters that Japan could build a nuclear weapon in as little as six months, and that it should consider doing so if trust in the U.S. nuclear umbrella broke down.

Japan has advanced nuclear know-how with a long-established fleet of civilian reactors, a sophisticated defense industry and technology from its space program, including solid-fuel rockets. This would allow it to build ballistic missiles to deliver a nuclear payload, experts say.

As a by-product of its nuclear fuel consumption, the government says Japan has about 45 tonnes of plutonium – the fissionable material needed to make a bomb. Japan also has the capacity to enrich uranium, another path to produce weapons-grade nuclear material.

South Korea has also developed and deployed a number of weapons that analysts say could deliver nuclear bombs – including a submarine designed to launch conventional ballistic missiles, and increasingly powerful missiles that could reach North Korea or China.

But South Korea is not as close to the threshold as Japan because it lacks the capacity to reprocess fuel to extract plutonium or enrich uranium, despite operating 26 reactors to generate power. Seoul aborted a clandestine weapons program in the 1970s under pressure from Washington and ratified the NPT in 1975. Experts predict it would take several years for Seoul to build a nuclear weapon, even if it overcame these hurdles.

“Even if we announce a state of emergency and throw all national resources behind it, the steelmaking, the facility building and making fissile materials and so on, it's not easy. I'd say four to five years,” said Cheon Myeong-guk, a researcher at the Korea Institute of Science and Technology.

Beyond the technical hurdles, other factors inhibit U.S. partners from developing their own nuclear weapons.

If Japan began to build a bomb in breach of its NPT commitments, it could face sanctions by the United Nations and lose access to the imported nuclear fuel it needs to feed its nuclear power industry. The densely populated archipelago also lacks an area suitable for nuclear testing.

Despite Trump’s earlier apparent openness to Japan and South Korea acquiring nukes, it remains unclear if his administration would ultimately agree. The State Department said Trump and Vice President JD Vance “have spoken frequently about their opposition to the spread of nuclear weapons.”

Beijing would be highly unlikely to remain passive if it learned that either Seoul or Tokyo were taking this path. A nuclear armed U.S. ally in East Asia could end up precipitating the conflict that acquiring nuclear weapons was intended to avoid, according to Alexandra Bell, a former Biden administration official who was directly involved in nuclear deterrence talks with Tokyo and Seoul.

“Having doubts about the U.S. commitment to extended deterrence and actually pursuing proliferation are two very different things,” Bell said. “The latter action would certainly provoke a response from the Chinese.”

Any move to acquire nuclear weapons might prompt China to further build up its nuclear stockpile or increase the likelihood of conflict if Beijing perceived such actions as being a prelude to war, she said.

China’s foreign ministry accused Japan and South Korea of “promoting so-called ‘extended deterrence’ to justify military expansion and military provocation.” Japan in particular, it told Reuters, claims to “advocate for a ‘nuclear-free world,’ while in reality relying on the U.S. ‘nuclear umbrella’ to cooperate with the deployment of U.S. strategic forces. These practices are hypocritical and self-contradictory.”

Japan’s evolving attitudes to the bomb have dismayed some survivors of the 1945 attacks.

Atomic bomb survivor Kunihiko Sakuma, 80, said he cannot understand that today a growing number of Japanese people are coming around to the view that nuclear weapons can offer protection, given the horrors he and others in Hiroshima experienced.

He was an infant when the bomb fell, curled up on a futon on the floor of his family home as his mother sorted the laundry. There was a flash and then suddenly everything went dark, his mother later recounted to him. She described how she had whisked him up and carried him on her back to a nearby shelter through a radioactive shower of soot and ash known as “black rain.”

“Just because we’re under the U.S. nuclear umbrella doesn’t mean we’re safe,” he said. “If nuclear weapons are used, it's over, isn't it. Real security only exists when there's mutual trust between nations.”