For the past 75 years, America’s nuclear umbrella has been the keystone that has kept East Asia’s great‑power rivalries from turning atomic.

President Donald Trump’s second‑term “strategic reset” now threatens to crack that arch.

By pressuring allies to shoulder more of the defence burden, hinting that US forces might walk^[1] if the cheques do not clear and flirting with a return to nuclear testing^[2], Washington is signalling that its once‑ironclad nuclear guarantee is, at best, negotiable.

In Seoul, Tokyo and even Taipei, a once-unthinkable idea — building nuclear weapons — has begun to look disturbingly pragmatic.

Nuclear umbrella starting to fray

Extended deterrence^[3] is the promise the United States will use its own nuclear weapons, if necessary, to repel an attack on an ally.

The logic is brutally simple: if North Korea contemplates a strike on South Korea, it must fear an American retaliatory strike, as well.

The pledge allows allies to forgo their own bombs, curbing nuclear proliferation while reinforcing US influence.

The idea dates to Dwight D. Eisenhower’s “New Look^[4]” military strategy, which relied on the threat of “massive retaliation” against the Soviet Union to defend Europe and Asia at a discount: fewer troops, more warheads.

Dwight D Eisenhower, when general of the US Army in 1943. Wikimedia Commons

John F. Kennedy replaced that hair‑trigger doctrine with a “flexible response^[5]” defence strategy. This widened the spectrum of options to respond to potential Soviet attacks, but kept the nuclear backstop in place.

By the 1990s, the umbrella seemed almost ornamental. Russia’s nuclear arsenal had rusted, China was keeping to a “minimal deterrent” strategy (maintaining a small stockpile of weapons), and US supremacy looked overwhelming.

In 2020, then-President Barack Obama’s Nuclear Posture Review^[6] reaffirmed the umbrella guarantee, though Obama had voiced aspirations^[7] for the long‑term abolition of nuclear weapons.

Barack Obama’s 2009 speech advocating nuclear disarmament in Prague.

The Biden administration then embraced a new term^[8] – “integrated deterrence”, which fused cyber, space and economic tools with nuclear forces to deter potential foes.

In recent years, however, North Korea’s sprint towards intercontinental ballistic missiles^[9] and the modernisation and expansion of China’s nuclear arsenal began testing the faith of US allies.

North Korean leader Kim Jong Un visits the Nuclear Weapons Institute in Pyongyang, North Korea, in 2023. KCNA/EPA

Trump has now turbo‑charged those doubts. He has mused that his “strategic reset” ties protection to payment. If NATO’s Article 5 (which obliges members to come to each other’s defence) is “conditional^[10]” on US allies paying their fair share, why would Asia be different?

Reports the White House has weighed a resumption^[11] of underground nuclear tests – and, under the Biden administration, even a more extensive arsenal^[12] – have rattled non‑proliferation diplomats.

A Politico analysis^[13] bluntly warns that sustaining global “extended deterrence” in two parts of the world (Europe and Asia) may be beyond Trump’s patience — or pocketbook.

A regional nuclear arms race

Allies are taking note. Last month, an Institute for Strategic Studies survey^[14] found officials in Europe and Asia openly questioning whether an American president would risk San Francisco to save Seoul.

In South Korea, public backing^[15] for a bomb now tops 70%.

Japan’s ruling Liberal Democratic Party is, for the first time since 1945, considering^[16] a “nuclear sharing” arrangement with the US. Some former defence officials have even called for a debate on nuclear weapons^[17] themselves.

Taiwan’s legislators — long muzzled on the subject — whisper about a “porcupine^[18]” deterrent based on asymmetrical warfare and a modest nuclear capability^[19].

If one domino tips, several could follow. A South Korean nuclear weapon program would almost certainly spur Japan to act. That, in turn, would harden China’s strategic outlook, inviting a regional arms race and shredding the fragile Nuclear Non‑Proliferation Treaty.

The respected international relations journal Foreign Policy has already dubbed^[20] Trump’s approach “a nuclear Pandora’s box.”

The danger is not just about more warheads, but also the shorter decision times to use them.

Three or four nuclear actors crammed into the world’s busiest sea lanes — with hypersonic missiles and AI‑driven, early‑warning systems — create hair‑trigger instability. One misread radar blip over the East China Sea could end in catastrophe.

What does this mean for Australia?

Australia, too, has long relied on the US umbrella without demanding an explicit nuclear clause in the ANZUS treaty.

The AUKUS submarine pact with the US and UK deepens technological knowledge sharing, but does not deliver an Australian bomb. Prime Minister Anthony Albanese insists the deal is about “deterrence, not offence,” yet the debate over funding nuclear-powered submarines exposes how tightly Australian strategy is lashed to American political will.

A regional cascade of nuclear proliferation would confront Australia with agonising choices. Should it cling to the shrinking US umbrella, invest in a missile defence shield, or contemplate its own nuclear deterrent? Any such move towards its own weapon would collide with decades of proud non‑proliferation diplomacy and risk alienating Southeast Asian neighbours.

More likely, Canberra will double down on alliance management — lobbying Washington to clarify its commitments, urging Seoul and Tokyo to stay the non‑nuclear course, and expanding regional defence exercises that make American resolve visible.

In a neighbourhood bristling with new warheads, middle powers that remain non‑nuclear will need thicker conventional shields and sharper diplomatic tools.

This means hardening Australia’s northern bases against a potential attack, accelerating its long‑range strike programs, and funding diplomatic initiatives that keep the Non-Proliferation Treaty alive.

The Trump administration’s transactional posture risks broadcasting a deficit of will precisely when East Asian security hangs in the balance. If Washington allows confidence in extended deterrence to erode, history will not stand still; it will split the atom again, this time in Seoul, Tokyo or beyond.

Australia has every incentive to prod its great power ally back toward strategic steadiness. The alternative is a region where the umbrellas proliferate — and, sooner or later, fail.

References

1. ^{^} forces might walk (www.reuters.com)
2. ^{^} return to nuclear testing (www.nytimes.com)
3. ^{^} Extended deterrence (www.iiss.org)
4. ^{^} New Look (www.britannica.com)
5. ^{^} flexible response (www.britannica.com)
6. ^{^} Nuclear Posture Review (ir.lawnet.fordham.edu)
7. ^{^} voiced aspirations (www.theguardian.com)
8. ^{^} new term (www.defense.gov)
9. ^{^} intercontinental ballistic missiles (www.bbc.com)
10. ^{^} conditional (www.nbcnews.com)
11. ^{^} weighed a resumption (www.stimson.org)
12. ^{^} more extensive arsenal (www.wsj.com)
13. ^{^} analysis (www.politico.com)
14. ^{^} Institute for Strategic Studies survey (www.iiss.org)
15. ^{^} backing (www.csis.org)
16. ^{^} considering (www.voanews.com)
17. ^{^} debate on nuclear weapons (asia.nikkei.com)
18. ^{^} porcupine (www.aspistrategist.org.au)
19. ^{^} modest nuclear capability (asiatimes.com)
20. ^{^} dubbed (foreignpolicy.com)