South Korea's diplomacy stands on shaky ground, as a leadership vacuum and the fallout from President Yoon Suk Yeol’s martial law debacle threaten to derail key foreign policy priorities -- among them, his Global Pivotal State vision and values-driven diplomacy --while risking the undoing of hard-won achievements. The turmoil has also drained the country’s vanishing political capital, further weakening its ability to steer its foreign policy agenda.

The Yoon administration was notably preparing for President-elect Donald Trump’s return to the White House in January, marking the 60th anniversary of Seoul-Tokyo diplomatic ties mended through leader-level initiatives, hosting the APEC summit and its first-ever summit with five Central Asian countries next year.

The absence of presidential leadership in foreign policy -- an area where Yoon has excelled compared to his domestic record -- became glaringly evident Sunday.

Ruling People Power Party leader Han Dong-hoon announced that Yoon "will no longer engage in state affairs, including diplomacy," as he transitions toward an "orderly early resignation" -- a day after surviving an impeachment motion over his contentious late-Tuesday-night martial law declaration.

Prime Minister Han Duck-soo also explained, "Maintaining the Korea-US alliance firmly and sustaining Korea-US-Japan cooperation robustly are very large and important tasks. The entire Cabinet, centered on the Foreign Minister, will do its best to preserve trust with the US, in Korea-US-Japan (relations), and with our partner countries."

However, the prime minister did not elaborate on how foreign policy would be managed in the absence of presidential authority during his joint news conference with the People Power Party leader.

Constitutional concerns

In South Korea, the president wields substantial power in foreign policy, a reflection of the country's presidential system and constitutional framework. Article 66(1) of the Constitution explicitly states, "The President shall be the Head of State and represent the State vis-a-vis foreign states."

The president plays a central role in direct diplomacy and foreign engagement, leading summits with foreign leaders, negotiating international treaties and appointing ambassadors.

Ha Shang-eung, a political science professor at Sogang University, emphasized that delegating presidential authority in foreign policy to unelected individuals is not only unconstitutional but also risks undermining South Korea’s international credibility.

"If the president is unable to effectively exercise their authority, and someone who was not elected by the people takes over those powers, or if the president has effectively stepped down, then in any case, having a ‘vegetative president’ play a role in foreign affairs is unconstitutional at its core,” Ha told The Korea Herald. "Moreover, how would other countries perceive this? I believe that is an extremely important consideration."

Joel Atkinson, a professor at the Graduate School of International and Area Studies at Hankuk University of Foreign Studies, interpreted the Han-Han joint news conference as a clear signal of intent to preserve the status quo in the Korea-US alliance and existing trilateral cooperation, while steering away from pursuing any new diplomatic initiatives.

"Yoon is now something worse than a lame duck. Anything he touches diplomatically will be undermined," Atkinson told The Korea Herald. "However, Han Dong-hoon and Han Duck-soo are emphasizing that there won’t be a vacuum, including in foreign policy. I take this to mean that the administration will be working to sustain what is going on rather than starting anything new."

Alliance under strain

However, the presidential vacuum in South Korea threatens to ripple through the Korea-US alliance at a critical moment, as Washington undergoes a power transition ahead of the inauguration of Trump's second-term administration. Renowned for prioritizing leader-level diplomacy, Trump's return had already spurred Yoon to seek an early in-person meeting, mirroring the efforts of leaders worldwide.

"But in this situation, if Trump takes office and our government expresses a desire to meet with him, do you think he would agree? He would likely rather respond with a question: 'Who am I supposed to meet with?'" Ha said.

Kim Heung-kyu, founder and director of the US-China Policy Institute at Ajou University, also pointed out that "the situation has unfolded with the advent of the Trump 2.0 era and a sharp increase in associated costs" when asked about the implications of a vegetative presidency for foreign policy.

"In the face of Trump's pressure, the Yoon Suk Yeol administration is likely to find itself in a position where it can do little but passively acquiesce. Because it cannot garner public support, there are no viable alternatives," Kim, president of the bipartisan think tank Plaza Project, told The Korea Herald.

"In the current climate, if the Yoon Suk Yeol administration continues to oversee foreign affairs and security, any such diplomatic and security efforts will be rendered entirely ineffective without the backing of public support."

Trilateral cooperation, Japan ties at risk

Yoon's precarious political standing casts a long shadow over his signature foreign policy initiatives, including his bid to strengthen trilateral cooperation -- a strategy deeply tied to Yoon-driven rapprochement with Tokyo. The initiative remains deeply contentious at home, as lingering historical grievances over Japan's colonial rule from 1910 to 1945 continue to draw sharp criticism from opposition parties.

"Japan, too, is unlikely to offer any diplomatic or economic concessions or support to the Yoon Suk Yeol administration, which is already facing criticism for its perceived handling of internal discord and declining public approval," Kim Heung-kyu said.

The immediate impact of South Korea’s domestic political turmoil on its relations with Japan is already becoming evident. Prime Minister Shigeru Ishiba’s potential visit to South Korea -- initially considered for January next year to mark the 60th anniversary of diplomatic normalization between Seoul and Tokyo -- may now be at risk due to the instability in Seoul, according to Kyodo News on Wednesday.

The trilateral partnership faces a triple whammy as Yoon’s political turbulence compounds existing challenges: Japan’s weakened Liberal Democratic Party under Ishiba, which failed to secure a majority in October’s snap elections, and Trump’s well-documented disdain for multilateralism.

"If President Yoon had focused, in the time he had left, on institutionalizing trilateralism and resisting impeachment inquiries it would have been challenging given the weakness in LDP and Trump's skepticism of multilateralism," Rob York, director for Regional Affairs at Pacific Forum, told The Korea Herald.

GPS becomes hollow

The critical issue lies in Yoon's damaged credibility overseas following his declaration of martial law.

"Yoon's credibility overseas has been undermined by declaring martial law, so he won't be able to exercise leadership in his foreign policies, especially when his days are numbered," Kim Duyeon, an adjunct senior fellow with the Indo-Pacific Security Program at the Center for a New American Security, said Saturday.

Among the most consequential casualties is Yoon's flagship foreign policy vision: positioning South Korea as a "Global Pivotal State," better known as GPS, committed to championing freedom, peace and prosperity worldwide. At the heart of this vision lies Yoon’s values-based diplomacy, aimed at forging deeper alliances with nations that share a commitment to liberal democracy and human rights.

"Yoon's foreign policy and the 'global pivotal state' with its rhetoric on freedom, democracy and the rule of law now ring hollow. The precariousness of his position will make all partners, including the US and Japan, very hesitant to associate and deal with Yoon," Jeffrey Robertson, an associate professor of diplomatic studies at Yonsei University in Seoul, told The Korea Herald on Saturday.

Yoon's martial law declaration and abrupt reversal six hours later sparked widespread condemnation at home and abroad, including sharp criticism from the US, as a backslide against democratic ideals and individual rights he has long claimed to uphold. The move was further criticized for its shaky justification.

"President Yoon's domestic political capital extends seamlessly to the international. Partners know that dealing with him will impact their reputation with the Korean people and likely hinder their capacity to deal with the next administration," Robertson added.

The long-term fallout from Yoon’s martial law declaration could resonate far beyond surface-level controversies, subtly eroding trust and stability beneath the diplomatic and economic security veneer.

"Other governments are still going to want to work with Seoul because South Korea is geopolitically and economically important," Leif-Eric Easley, professor of international studies at Ewha Womans University in Seoul, told The Korea Herald.

"But for some time, there may be unspoken limits on cooperation, even after this administration. When democracy is tested to the extent of damaging public trust, diplomatic and investment partners inevitably update their risk assessments."

Kim Duyeon stressed that South Korea must uphold its foreign policy commitments despite the presidential crisis, as the country's global role surpasses its leader.

"As difficult as it will be because of the crisis in South Korea's presidential leadership, its government bureaucracy will need to continue implementing existing alliance and foreign policy initiatives as best it can because there is a lot of important work to do globally and a country does not equal one person in its highest office," she told The Korea Herald on Saturday.

"This is surely a tricky task, but the government will need to try to project some normalcy in its international relations and contributions because there are pressing global security issues to deal with."