Trump tariffs and nuclear diplomacy test South Korea-US alliance

South Korea’s long-standing alliance with the United States is showing signs of fracture, as new trade tensions and political uncertainty in Seoul collide with President Donald Trump’s unpredictable approach to foreign policy. At the heart of the strain is Trump’s imposition of a 25 percent “reciprocal” tariff on Korean imports, which has caught South Korean leaders off guard and deepened concerns about Washington’s broader regional strategy, the Financial Times reported.

South Korean officials initially believed their comprehensive free trade agreement with the US would shield them from tariff action. But Trump’s March State of the Union address dispelled that notion, as he accused Seoul of unfair trade practices — falsely claiming it levied four times the tariffs the US did — and followed up with duties on steel, automobiles, and potentially semiconductors and pharmaceuticals.

A fragile government at home

Seoul’s response has been weakened by ongoing domestic political turmoil. President Yoon Suk Yeol’s declaration of martial law in December triggered a constitutional crisis, culminating in his removal from office in April. His successors — acting president Han Duck-soo and finance minister Choi Sang-mok — both resigned this month, leaving the country in the hands of a caretaker government ahead of presidential elections.

The frontrunner in those elections, opposition leader Lee Jae-myung, has called the US an “occupying force” and is pushing for a softer line on China. That stance raises the risk of a shift in South Korea’s foreign policy, particularly as the Trump administration intensifies its focus on China and Taiwan, rather than North Korea.

Trump’s unpredictable North Korea diplomacy

Trump’s desire to reopen talks with North Korean leader Kim Jong Un is raising alarm in Seoul, where officials fear a repeat of his first-term summit diplomacy that sidelined South Korea entirely. Trump has praised Kim in recent statements and described North Korea as a “big nuclear nation,” prompting speculation that he may be open to a deal that freezes Pyongyang’s intercontinental missile program while leaving its short-range arsenal — a direct threat to the South — intact.

Experts like Jenny Town at the Stimson Center warn that such a deal would be a worst-case scenario for Seoul: it would protect the US homeland while leaving South Korea vulnerable to nuclear blackmail. If that happens, some in Seoul say the country may have no choice but to consider acquiring its own nuclear weapons.

US pressure and shifting defence priorities

Adding to the pressure, the Trump administration is pushing South Korea to shoulder more of the financial burden of hosting 28,500 US troops, with a proposed 8.3 percent increase in its annual contribution. But more significant is the shift in US defence strategy. Officials suggest

America’s priority is now China, not North Korea, and that Seoul may soon be expected to take “overwhelming responsibility” for its own defence.

South Korean policymakers are increasingly concerned that they are being asked to do more militarily while receiving less in economic and diplomatic assurance. As Victor Cha of CSIS put it, “The alliance is in a state of quiet crisis — but the crisis is unlikely to remain quiet for long.”