Commentary: Trump’s South Korea defence flip reminds Japan it has no Plan B
While alarming for Seoul, an abandonment of US guarantees could be disastrous for Tokyo, says Leo Lewis for The Financial Times.
Japanese Prime Minister Sanae Takaichi gestures as US President Donald Trump delivers his speech during their visit to the aircraft carrier USS George Washington at the US Navy’s Yokosuka base in Yokosuka, south of Tokyo, Oct 28, 2025. (AP Photo/Eugene Hoshiko, File)
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TOKYO: On Wednesday night (Aug 19), after a summer of sharply escalating regional tension, protesters lined the roads near Sanae Takaichi’s residence bellowing pleas for the Japanese prime minister to stick to pacifism under the “peace clause” of the country’s constitution.
Unspoken, as always on these occasions, was an acknowledgment that this clause is underwritten by one of the most enduring and unambiguous Plan A’s in postwar geopolitics. Namely that, should a serious threat emerge, pacifist Japan can rely on the military protection of the United States under the 1951 alliance between the two countries.
That’s 75 years not just without a Plan B, but with a unique constitutional constraint on conceiving one.
But Monday’s chessboard-tipping social media post by US President Donald Trump, calling for a reduction in joint US military exercises with South Korea, casts all this in a very different light, however fleeting the pivot proves and however fulsome the backroom reassurances Washington is currently breezing out to Japan and other nervous allies.
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For while Seoul bore the most obviously destabilising impact of Trump’s diplomatic sucker punch, in which he ordered an out-of-the-blue cut “based on my very good relationship with Kim Jong Un”, there is arguably more long-term jeopardy for Japan.
If US guarantees come to look genuinely shaky, South Korea must recalibrate; Japan, under the same circumstances, must reconstitute.
A SYMPTOM OF A SHIFT
Any question over US reliability is profoundly alarming: For all the arguments that this is just a Trump pathology, there is the plausible thesis that he is merely a symptom of a far less reversible shift.
It still, just about, feels premature to panic. Tokyo, along with other US ally capitals, has been finding its sea legs amid the churn of on-the-run foreign policy redrafting and evidently has internal mechanisms for separating wheat from chaff.
It has also played the Trump game pretty well, expediting a US$550 billion pledge to invest in the US and moving relatively quickly to present itself as an indispensable partner in critical supply chains and production of military equipment.
But Monday’s post, which cheerfully juxtaposed the central announcement with a reminder that Seoul had not joined America’s war on Iran, demanded to be read as an abrupt departure from conventional US calculus around regional stability, its core interests and the wisdom of linking multiple diplomatic issues.
PUBLIC DEMAND FOR PLAN B
The problem with Japan’s Plan A is twofold. The first, which had seemed remote until this Trump term, is its vulnerability to US reliability.
The second has been that the country’s commitment to both its pacifist constitution and the alliance has made serious consideration of a Plan B nearly impossible – whether that be conventional rearmament, national service or contemplation of a nuclear deterrent.
Earlier this month, Japan published its annual Defense of Japan white paper. This pledged that by fiscal 2027, Japan would have strengthened its capabilities to the point where it could take “primary responsibility” for dealing with an invasion, though with US support.
This takes the country a very significant distance, conceptually, from where it was 10 years ago but it remains, say analysts, some way from being a Plan B.
All of this may suit Takaichi very well, as Japan’s sense of beleaguerment intensifies. Since the start of her premiership, the argument for the country to start thinking more radically about its defence, and for the public to embrace the debate, has been repeatedly made for her by others.
Almost from day one, China cast her as a re-militarisation-hungry fanatic in a way that has made Beijing look the more unreasonable. North Korea, meanwhile, has actively supported Russia against Ukraine while significantly escalating its anti-Japanese rhetoric, accusing Tokyo of fostering a “nuclear alliance” with South Korea and the US.
Earlier this month, Vladimir Putin paid his first-ever visit to one of four islands disputed between Russia and Japan, reviving Japan’s consciousness of another potential foe on its doorstep.
But the final, and perhaps most influential, card has now been played by Japan’s closest ally – not just through Trump’s Truth Social post, but the rapid erosion of norms that leaves nobody exactly sure how seriously to take his proclamations.
The protesters outside Takaichi’s residence were a reminder of the constraints that have bound her predecessors from tampering with Plan A. August 2026 has reminded her how suddenly the public may demand a Plan B.
Source: Financial Times/el
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