President Yoon Suk Yeol bows after apologizing to the public for causing concerns and inconvenience due to his martial law declaration, during a televised address at the presidential office in Seoul, Saturday. Courtesy of presidential office

South Korea's summit-level diplomacy is at a standstill after President Yoon Suk Yeol de facto lost his governance power in the aftermath of his short-lived martial law.

Although Yoon escaped impeachment, his political career appears cut short, as the ruling People Power Party (PPP) has officialized the president's “early resignation," Sunday.

In the meantime, Prime Minister Han Duck-soo is expected to take on the role of managing state affairs. However, under the leadership of Han, whose legal authority in the diplomatic realm remains unclear, significant challenges lie ahead for the nation's diplomacy.

In a joint briefing with the prime minister, Sunday, PPP leader Han Dong-hoon said his party will “pursue an orderly resignation” of Yoon. This means that the president is expected to step down before his five-year term ends in 2027.

“There will be no confusion during the orderly early resignation process,” Han said. “Even before stepping down, the president will not be involved in state affairs, including diplomacy.”

The prime minister vowed continuity of diplomatic efforts.

“Maintaining the strength of the South Korea-U.S. alliance and solidifying trilateral cooperation between South Korea, the U.S., and Japan are very important tasks. The entire Cabinet, led by the foreign minister, will do its utmost to preserve trust in our relationships with the U.S., Japan and other allies,” he said.

These developments come after the National Assembly failed to pass a motion to impeach Yoon on Saturday evening. The motion was nullified when 105 of the PPP's 108 lawmakers boycotted the vote, leaving the Assembly short of the required quorum of 200 votes.

People rally at the National Assembly in Seoul, Saturday, calling for the passage of the impeachment motion against President Yoon Suk Yeol. Korea Times photo by Shim Hyun-chul

The impeachment motion was in response to Yoon's surprise martial law declaration on Tuesday. The emergency military rule, which lasted for only six hours, thrust the already-unpopular president's political career to the rock bottom.

As the president steps aside from state affairs, the prime minister is expected to assume most of his domestic and diplomatic duties. But uncertainties linger regarding how the nation can navigate its diplomatic agenda with its image tarnished following the martial law debacle.

2025 is a pivotal period for South Korea's foreign relations.

Efforts had been underway to arrange a meeting between Yoon and incoming U.S. President Donald Trump, while Japanese Prime Minister Shigeru Ishiba was reportedly considering a visit to Seoul in January — both plans now in jeopardy due to the political turmoil.

Additionally, South Korea is set to host the Asia-Pacific Economic Cooperation (APEC) summit in Gyeongju next October, a major event expected to attract around 20 world leaders and thousands of delegates. The APEC summit has been regarded as a key opportunity to revive the long-stalled summit diplomacy with China, as the two nations have been actively discussing Chinese leader Xi Jinping's participation.

President Yoon Suk Yeol and Kyrgyz President Sadyr Japarov shake hands during a summit held at the presidential office in Seoul, Tuesday. Hours after the meeting, Yoon declared martial law in a surprise briefing. The Kyrgyz leader, who was in South Korea when the emergency military rule was announced, canceled his remaining schedule and returned home the following day. Yonhap

But all these efforts are in peril amid a leadership vacuum.

"With the U.S. showing reluctance to further engage with the Yoon administration, this could be the end of South Korea's diplomacy under the current government," a diplomatic analyst in Seoul said on condition of anonymity.

“The U.S. has been openly critical of Yoon's martial law attempt. Under such circumstances, other like-minded nations will also be reluctant to engage with South Korea. The best we can do under the prime minister is to show the international community how Yoon's resignation happens in a peaceful, democratic manner."

After the failed impeachment vote, Sunday, the U.S. administration called for the "proper functioning of South Korea's democratic processes."

“We continue to call for the full and proper functioning of the ROK's democratic institutions and processes, in accordance with the Constitution,” a U.S. official was quoted as saying by Yonhap News Agency. ROK stands for the Republic of Korea, South Korea's official name.

“The right to peaceful protest is an integral element of a healthy democracy and must be respected in all circumstances,” the official added.

In a phone call with Foreign Minister Cho Tae-yul on Friday, U.S. Secretary of State Antony Blinken expressed his expectation for "the democratic process to prevail," a remark some analysts interpreted as subtle support for Yoon's ousting.

French President Emmanuel Macron welcomes U.S. President-elect Donald Trump for the reopening ceremony of the Notre Dame de Paris Cathedral in Paris, Saturday (local time). EPA-Yonhap

Seoul's diplomacy with the incoming Trump administration has become trickier.

While Trump has not publically reacted regarding the martial law fiasco, his diplomatic approach preferring high-profile leader summits suggests that he may not be willing to engage actively with South Korea's weak president.

Yang Moo-jin, president of the University of North Korean Studies, said Yoon's diminished credibility will bring a long-lasting strain on the nation's foreign relations.

“Credibility and predictability are the most important factors in diplomacy. A leader must have public support to advance their agenda on the international stage. Yoon has lost his leverage in summit diplomacy,” he said.

Yang also commented that the martial law saga has added uncertainty to the security situation surrounding the Korean Peninsula. North Korea has so far remained silent on the political turmoil in the South, though Yang believed this quiet period will not last long.

“The Kim Jong-un regime is likely to use the incident as a propaganda tool to claim that South Korea's political system is fragile, while describing their system as more stable and secure,” he said.