The political upheaval sparked by President Yoon Suk Yeol’s abrupt declaration of martial law -- issued without prior notice to the United States and rescinded just six hours later -- has heightened uncertainties in the South Korea-US alliance, already strained by Donald Trump's return to power.

Leadership transitions in both Seoul and Washington amplify the turbulence. Even if Yoon survives the political storm, his foreign policy achievements -- outshining his domestic track record -- and his significant investment in the alliance are likely to be overshadowed and lose momentum amid growing pressure to focus on domestic challenges.

While experts view the alliance as stable for now, anchored by US priorities to uphold stability on the Korean Peninsula and counter China, prolonged political instability in Seoul risks eroding trust in Washington, jeopardizing the alliance’s long-term trajectory.

"The alliance and the ROK already faced a very uncertain future with the transition from Trump to Biden, including a significant turnover not only in personnel and regular alliance management processes but also in the worldview and policy priorities of the new personnel coming into office in Washington," said Clint Work, a fellow at the Korea Economic Institute of America, speaking to The Korea Herald in a personal capacity, not representing the views of the organization.

The ROK is the official name of South Korea, the Republic of Korea.

"Ironically, it could become even more uncertain if the alliance faces a similar situation to what it faced at the outset of Trump's first term."

Work further explained that should Yoon be impeached and removed from office, it is not only possible but also highly likely that a progressive South Korean administration would take power just at the same time Trump undertakes a US policy review toward Korea and the alliance.

"It is entirely too early to say with any certainty, but yesterday's events may have set in motion a process whereby within 6-9 months, the alliance could face a cacophonous set of changes," Work said.

Minimal fallout for now

Despite these concerns, some experts foresee minimal immediate impact on the alliance, suggesting that Washington is likely to downplay the incident and maintain its focus on strategic objectives.

"Put simply, Washington doesn't want to see further domestic tumult and instability but is above all concerned about strategic stability on and around the peninsula," Work said.

Karl Friedhoff, a fellow at the Chicago Council on Global Affairs, said "The United States will make every effort to pretend this didn’t happen so it can continue to try to pull Korea into the competition with China."

Mason Richey, a professor at the Graduate School of International and Area Studies of Hankuk University of Foreign Studies said "At least in the short term, the US-South Korea alliance will remain stable in its core mission to deter external aggression against South Korea."

"In the medium and long term, however, the imposition of martial law and follow-on political chaos is likely to undermine the argument that the US-South Korea alliance is based on the values of liberalism and democratic civil values."

A White House National Security Council spokesperson emphasized Tuesday that "Democracy is at the foundation of the US-ROK alliance," in a statement on Yoon’s decision to rescind the declaration of emergency martial law.

In a separate statement, US Secretary of State Antony Blinken echoed the sentiment, affirming, "We reaffirm our support for the people of Korea and the US-ROK alliance based on shared principles of democracy and the rule of law."

Richey warned that "political instability in Korea will, in some way and over some time frame, damage the US's trust in South Korea as an alliance partner."

Alliance losing momentum

Andrew Yeo, the SK-Korea Foundation Chair at the Brookings Institution's Center for East Asia Policy Studies, observed that while the alliance remains resilient and commands bipartisan support from leaders of both the ruling and main opposition parties, its perceived strength may have waned compared to the early years of President Yoon's tenure -- assuming he remains in office.

"I anticipate growing voices for impeachment and greater political instability in the coming days which will make it harder for the Yoon government to put its best foot forward in navigating the political transition from Biden to Trump," Yeo said.

"The Trump administration may not care that Yoon invoked martial law, but the ability to move alliance relations forward requires domestic support and legitimacy."

A majority of experts speaking to The Korea Herald noted that the likelihood of the main opposition Democratic Party of Korea gaining control, sooner or later, could signal a shift in Seoul’s stance, making it less supportive of the South Korea-US alliance and introducing greater ambiguity in its strategic position amid intensifying US-China competition.

"The bigger question will be who comes after Yoon. The answer to that question could have important effects for the alliance," Friedhoff said.

"How Trump will react to this is anyone’s guess. I think the more important part to alliance relations will be who the South Korean president is. If it is indeed Lee Jae-myung, he will feel the need to stand up to the United States, and that could create quite a bit of instability moving forward."

Global ambitions undermined

Experts also highlighted that the political turbulence triggered by Yoon’s declaration of emergency martial law — the first such action since 1979 — risks tarnishing South Korea’s international standing. It could undermine Seoul’s foreign policy aspirations to position itself as a "global pivotal state" and a vanguard of liberal democratic values and the rules-based international order.

"Yoon spent much of his first two-and-a-half years cultivating and strengthening the US-South Korea alliance to help anchor his global pivotal state strategy," Yeo said.

"The sudden, brash, and somewhat inexplicable decision to declare martial law suddenly makes the idea of values-based diplomacy and South Korea's role as a global pivotal state look hollow."

David Maxwell, vice president of the Center for Asia Pacific Strategy and a retired US Army Special Forces colonel, underlined that, "We cannot say this is solely a domestic issue especially after South Korea has postured itself to be a global pivotal state."

"Its internal politics have external effects."

Kim eyeing opportunities

Experts also emphasized the risk of North Korean leader Kim Jong-un exploiting political turmoil in South Korea, the power transition in Washington, or potentially simultaneous leadership changes in both Seoul and Washington.

Work said, "At a time when the Yoon administration is facing resignations from key positions, widespread opposition, and potential impeachment, it would not be difficult for Pyongyang to inject even greater instability and exploit domestic fissures in Seoul and within the alliance."

Patrick Cronin, the Asia-Pacific security chair at Hudson Institute, warned that "a weak leader with a wobbly economy and domestic strikes and protests would be welcome news to Kim Jong-un and competitors."

Maxwell cautioned that Yoon's declaration risks creating opportunities for Kim Jong-un to exploit, potentially inciting violence and prompting miscalculations by South Korean security forces that could escalate tensions.

Maxwell also noted that Yoon's declaration of emergency martial law could undermine his administration’s human rights advocacy against North Korea, inviting "whataboutism" from the Kim Jong-un regime.

"My concern is with how to affect and adjust an information campaign against the North. And ultimately my concern is with the impact on the pursuit of a free and unified Korea. This will certainly undermine the 8.15 unification doctrine," Maxwell said.