Key Takeaways:
- The U.S.–ROK alliance in 2025 is defined by unprecedented uncertainty, with fragmented leadership in both Washington and Seoul, escalating transactional demands, and conflicting interpretations of summit outcomes.

- Trump’s revived skepticism of alliances and push for greater South Korean defense and financial commitments—paired with Seoul’s pursuit of nuclear-powered submarines—has opened major strategic, political, and proliferation questions.

- As both sides debate broader Indo-Pacific roles and China policy, the alliance now operates in a “Schrödinger’s” state: simultaneously vital and vulnerable, strengthened in rhetoric yet weakened by mistrust, ambiguity, and mismatched expectations.

2025 has been a tumultuous year for the U.S.-South Korean alliance with new leadership in both countries repudiating the policies of their predecessors while yet to clearly define their own. Both the Donald Trump and Lee Jae-myung administrations are fragmented with factions advocating competing policy viewpoints, adding to the uncertainty from Trump’s erratic and unpredictable decision-making process.

Trump’s reelection brought a return of his dismissive attitudes toward the utility of America’s alliances as well as exponentially ramping up his transactional demands on security and economic partners. Having bullied Seoul into a disadvantageous trade deal that violated the U.S.-South Korea free trade agreement and possibly the U.S. Constitution, the Trump administration demanded commensurate security concessions.

Mid-year media reports indicated the U.S. was considering reducing its forces in South Korea and reorienting their primary mission toward defending Taiwan while requiring Seoul to increase its defense spending and pledge a role against the growing China military threat to the Indo-Pacific.

There was great trepidation before the first Trump-Lee summit in August. President Lee later commented that his staff had been worried of a “Zelenskyy moment,” a reference to the disastrous meeting that Ukrainian President Volodymyr Zelenskyy had with Trump in February 2025.

That the fears of disaster were not borne out is due to a combination of the forecasts having been excessively dire, Lee’s masterful sycophancy during the summit meeting, that Trump’s threatening rhetoric was just part of ‘the art of the deal,’ that the prioritizer faction in the Trump administration has been weakened, and “Trump Always Chickens Out” whereby threats are modified when faced with resistance.

The bilateral statements after the second Trump-Lee summit in October are a Rorschach test open to interpretation over how significant a difference they represent from previous bilateral agreements. The absence of long-standing phrases that had been present in previous declarations was interpreted as diminution of the U.S. commitment to its ally.

Conflicting post-summit statements by U.S. and South Korean officials indicate divergent perceptions as to what may have been agreed to. The vagueness of phraseology suggests that the devil is not yet in the details since much needs to resolved on both security and economic topics.

The biggest surprise announcement from the summit meetings was U.S. acquiescence to Seoul’s long-standing quest for permission to build nuclear-powered submarines. Lee depicted his request as empowering South Korean naval capabilities to reduce the defense burden of the United States. Lee also requested South Korea be allowed to reprocess spent nuclear fuel and enrich uranium which are currently prohibited under the bilateral civilian nuclear agreement (often referred to as the 123 agreement).

Washington had resisted decades of previous South Korean requests for both nuclear-powered submarines and loosening the civilian nuclear agreement due to concerns of the potential for nuclear proliferation. There is speculation that the South Korea request for nuclear-powered submarines was a Trojan Horse to gaining revision of the civilian nuclear agreement and potentially achieving “nuclear latency” as a step toward developing an indigenous nuclear weapons program.

There are extensive doubts over the utility of South Korean nuclear-powered submarines since their main benefit is to provide a longer operational range than conventionally-powered submarines, a capability not needed against North Korea’s coastal naval threat. Instead, it appears that nuclear-powered submarines are a vanity project based on national pride, particularly after U.S. ally Australia was allowed to acquire nuclear-powered submarines.

The South Korean nuclear-powered submarine program would be extremely expensive, forcing tradeoffs with other more important security enhancements, including those necessary for attaining wartime operational control of South Korean forces, which the Lee administration has defined as a critical security objective during its five-year term. The program could also detract from the new alliance emphasis placed on South Korean assistance to redressing serious shortfalls in the U.S. ability to build sufficient naval forces to compete against the escalating Chinese seaborne threat.

In extolling the virtues of nuclear-powered submarines for South Korea, President Lee inadvertently opened a door that he likely wished to remain closed. When appealing to Trump, President Lee commented that Seoul’s existing submarines were limited in their ability against North Korean and Chinese submarines.

Hinting at an anti-China mission for the South Korean navy aligns with U.S. advocacy for Seoul to assume a greater Indo-Pacific security role but clashes with Seoul’s historic aversion to aggravating Beijing. Chinese economic retaliation against Seoul’s 2017 decision to accept the deployment of the US THAAD anti-missile defensive system has had a lasting impact on South Korean timidity in even directly criticizing Chinese egregious actions.

U.S. officials continue to push for a South Korean role in constraining China. Admiral Daryl Caudle, the U.S. chief of naval operations declared it would be a “natural expectation” by Washington for South Korea to utilize nuclear-powered submarines to play a role in countering China. Caudle posited that “with great power comes great responsibility [for] Korea to deploy those submarines globally and move away from just being a regional navy.”

Similarly, General Xavier Brunson, Commander of U.S. Forces Korea, depicts South Korea as a vital cog in U.S. Indo-Pacific strategic for deterring and confronting regional threats including China. In a recent article, he used a reoriented Indo-Pacific map placing East at the top to emphasize the strategic geographic location of South Korea and U.S. forces stationed there to conduct military strikes against North Korea, China, and Russia, including China’s Northern Theater Army and Northern Fleet as well as the Russian fleet in Vladivostok.

The altered map viewpoint also underscores, Brunson argues, the emergence of a strategic network connecting Korea, Japan, and the Philippines to provide complementary security capabilities against common threats. A senior South Korean military official quickly dismissed scenarios of direct South Korean military operations against China or Russia as “not realistic” and emphasized that Seoul does not endorse interpretations implying a regionwide mission shift.

There is now a Schrödinger's alliance between Washington and Seoul with differing assessments of its vitality. The relationship is being challenged by the uncertainty of both nations’ Indo-Pacific policies, competing national objectives, and President Trump’s willingness to risk long-standing alliances in favor of transactional economic gains.

Washington is demanding more and promising less to its security and economic partners. Allies now perceive a price tag for America’s adherence to alliance treaty commitments and severe punishment for any aversion to pay it. The U.S. may have degraded military deterrence by undermining the perception – in the minds of both allies and opponents – that Washington is a dependable security partner.