Donald Trump’s disdain for the US’s traditional partners is emerging as a central feature of his administration’s foreign policy. Washington’s Indo-Pacific allies have so far avoided such ire but Trump will eventually turn toward them – and likely pick the same fights that he has with Europe. South Korea seems particularly vulnerable because it has the two characteristics that Trump dislikes most in American allies: a large, expensive US security commitment and a substantial trade surplus. Japan has these traits too but a Trumpian assault on Tokyo would jeopardise the entire US position in East Asia, so Seoul will likely come first. 

During his first term, Trump’s treatment of South Korea was brusque and dismissive. In 2017 he notoriously threatened to rain “fire and fury” down on North Korea. Then in 2018, he suddenly declared North Korean dictator Kim Jong-un his friend and met him three times. Throughout all of this, Trump ignored South Korean input and concerns. The US president’s 2017 war threats were not cleared with Seoul and unnerved then-South Korean president Moon Jae-in so much that he publicly stated that no military action could be taken against North Korea without the South’s permission. This norm had always been informally understood within the alliance because South Korea would carry most of the costs of any conflict. Trump characteristically ignored that tacit understanding.

Similarly, when Trump and Kim negotiated in 2018 and 2019, Moon and the South Koreans were explicitly cut out. The Trump administration did not clear any proposals made to Pyongyang with Seoul and Moon was never invited to any of the summits with the US president in attendance. Indeed, Trump later attacked Moon in the US media, stating that he intended to “blow up” the US-South Korea alliance if re-elected. Trump’s foreign policy has become even more vindictive in his second term. The US president gleefully trolled former Canadian prime minister Justin Trudeau with suggestions that his country should be annexed. And Trump’s falling out with Ukrainian president Volodymyr Zelensky seems mostly motivated by the latter’s refusal to grovel before him on camera. When Trump eventually turns to South Korea, it is reasonable to expect that his behaviour will be even worse than last time. South Korean officials and foreign-policy intellectuals are already preparing for this eventuality. Among other things, a previously niche South Korean debate on nuclearisation has grown dramatically since Trump’s arrival on the US political scene.

South Korea is particularly vulnerable to Trumpian threats. Like Poland or the Baltic states, it is a front-line democracy adjacent to a belligerent, nuclear autocracy; two, in fact: North Korea and China. Some 28,000 US troops stationed in the country have back-stopped South Korea’s rapid economic growth while acting as a tripwire to contain North Korea. Every US president since Harry Truman has supported this commitment. Trump, judging by his behaviour in Europe and general affection for dictators, does not. The US is still committed by treaty to South Korean security – as it is to Nato. But just as Trump seems unlikely to cleave to the Transatlantic Alliance’s collective-security guarantee, he is also likely to abandon South Korea should it become embroiled in a major conflict with North Korea or China.

Seoul’s response will probably mirror what European leaders have also declaimed over the past few months: major rearmament. Unlike Europe, South Korea has the industrial bases and defence manufacturers to rapidly churn out a large number of high-quality munitions. More controversial, however, will be the inevitable nuclear debate. South Korean public opinion has been strongly in favour of acquiring nuclear weapons for at least 15 years – a 2023 poll put the figure at 76 per cent. Political opinion is slowly tilting this way too, though it has been restrained by both intense US opposition and Washington’s support for the Non-Proliferation Treaty (NPT), intended to block the spread of nuclear weapons. Given its disdain for multilateral commitments, the Trump administration is unlikely to care much about the NPT. Since many in Seoul now believe that the US would not come to South Korea’s aid against its nuclear-armed autocratic opponents, the logical step is for the country to develop its own weapons. This would act as a demonstration for exposed US allies – most obviously Poland – to do the same. Trump is ushering in a world of nuclear proliferation – and he does not seem to care. 

Robert E Kelly is a professor of political science at Pusan National University.