The anxiety gripping Seoul is palpable. Under US pressure, South Korea signed a US$350 billion investment deal last November for a 10-percentage-point tariff reduction, billing it as a strategic alliance. Barely a year on, the facade has crumbled. Last month, US President Donald Trump announced a US$200 billion tranche of the deal with no South Korean official present. Blindsided, Seoul restated its “commercial viability” clause. Trump’s response was blunt. “If they don’t want to do it, that’s...