The Koreas | Security | East Asia

South Korea’s Nuclear Ambitions Clash With Political Realities

South Korea’s ruling party failed to secure key races, underlining the need to steer the country’s nuclear future with more than just political momentum.

In the first week of June, two seemingly unrelated events took place in Seoul. On June 3, U.S. and South Korean officials met to discuss the implementation of South Korea’s civilian reprocessing and enrichment program. The same evening, Seoul’s conservative mayor Oh Se-hoon was re-elected. Coincidental though they may be, the events should serve as a reminder that South Korea’s nuclear and political futures are tightly intertwined.

South Korea’s Nuclear Future

In September 2025, the United States broke with a long-term policy practice and expressed support for South Korea’s ambitions to acquire uranium enrichment and reprocessing, intended to secure Seoul’s supply of nuclear fuel, and improve its management of spent fuel. 

The announcement came as a big surprise. Ever since the United States uncovered South Korea’s secret nuclear weapons program in the 1970s, it had blocked Seoul from acquiring these technologies because they can also be used in nuclear weapons production. In April 2025, only a few months before the surprising announcement, the U.S. Department of Energy had designated South Korea a “sensitive country,” a designation usually reserved for nuclear proliferators like Syria, Iran, and North Korea. Ostensibly, the designation was the result of a South Korean national’s involvement in industrial espionage against U.S. companies. But members of the progressive Democratic Party (DP), in political opposition at the time, were quick to attribute it to the past few years of mostly conservative politicians calling for Seoul to acquire nuclear weapons.

What changed? In the intervening months, South Korea held a snap-election to replace the impeached president Yoon Suk-yeol, who had been the first South Korean president to broach the nuclear topic in public (statements he later walked back). The progressive Lee Jae-myung swept to victory in the June 2025 elections, and high-level members of his Cabinet swiftly set to the task of denying that South Korea would ever pursue nuclear weapons ambitions on their watch. In an essay for Seoul-based think tank Asia-Pacific Leadership Network, Foreign Minister Cho Hyun called non-proliferation “a strategic imperative” for South Korea.

Lee himself has argued in public, most recently on June 8, that South Korea would not be able to endure the international sanctions that would befall it if it were to go nuclear at some point in the future.

At the political level, the Lee administration has thus made extensive efforts to refute and tone down any talk of nuclearization. The president also enjoys historically high – if declining – approval ratings, and his party just took home 12 out of 16 mayoral and gubernatorial seats in recent local elections. Nuclear issues are admittedly far too niche to decide electoral outcomes in South Korea, but Lee would appear to have a broad mandate to shape South Korean nuclear policy well into the future.

But political winds can change fast in South Korea. And Lee may be sowing nuclear seeds in political soil that could yet shift rapidly under his feet. 

South Korea’s Political Future

Such a shift may already be apparent from one crucial district that the DP did not carry in the recent local elections: the capital city itself. The conservative mayor of Seoul, Oh Se-hoon, beat Lee’s handpicked candidate to win his third consecutive term in office (and fifth in total).

Oh is a veteran politician, with a record of skillfully navigating the Korean political landscape and staging comebacks. He wisely distanced himself from former president Yoon and the infighting that followed his impeachment. Despite being seen as a promising presidential contender, Oh refrained from throwing his hat in the conservative race ahead of the 2025 snap election, recognizing that it was set to deliver an inevitable wipeout victory to the progressives. Instead, he stayed fast in his mayoral seat.

That strategy appears to have paid off. While he was widely predicted to lose his mayoral race, Oh made a late election night comeback, bucking the nationwide trend that routed conservative candidates in most other districts.

Oh’s victory should give pause to anyone who expects the progressive electoral successes to keep piling up in the years ahead. Recent history supports this prediction: The 2020 National Assembly elections were another landslide win for the DP, and nobody at the time would have predicted that a conservative candidate would win the presidency just two years later.

But Oh is not just a future presidential hopeful. He also has a mixed record as far as his views on South Korea’s nuclear future go. In 2019, he called........

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