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 if the cheques do not clear and flirting with a return to nuclear testing, 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.
Extended deterrence is the promise that 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.
