The Republic of Korea (ROK) President Yoon Suk Yeol’s attempted self-coup in December 2024 sent shockwaves through the Indo-Pacific region. On April 4, the Constitutional Court of Korea unanimously upheld Yoon’s subsequent impeachment by the ROK National Assembly. As a result, South Korea will now hold an early presidential election to replace Yoon within 60 days.
Yoon drew attention for his intrepid attempts to forge deeper security partnerships with the United States and Japan. His anticipated removal has unnerved Tokyo, which benefited from a rapprochement with Seoul after the tumultuous years under former ROK President Moon Jae-in. Meanwhile, Taiwan is concerned that the next ROK president may not emulate Yoon’s forward-leaning approach to countering the People’s Republic of China’s (PRC) expansionist ambitions in the Indo-Pacific.
There is no certainty regarding the winner of the ROK’s early election. While the opposition Democratic Party (DP) remains roughly as popular as the ruling People’s Power Party (PPP), the DP leader Lee Jae-myung far surpasses any PPP challenger in preliminary head-to-head presidential polling. A third-party candidate could possibly emerge to steal the election away from the two main parties, but it is more likely that this candidate would split the conservative vote and hand Lee Jae-myung an easy victory. Therefore, it is worthwhile for stakeholders in Taiwan policy to plan for victory by Lee and the Democratic Party.
Image: Lee Jae-myung, the leader of the ROK’s Democratic Party (Image source: Wikimedia Commons)
A Zenith of Multilateral Security Cooperation under Yoon
Taiwanese people will remember Yoon’s presidency as a time when the ROK unabashedly embraced partnerships with Japan and the United States to counter rising threats from China, Russia, and North Korea. The Yoon Administration adopted a rhetorical stance that was more assertive than its predecessors, calling the North Korean regime an “anti-nation, anti-historical group” and threatening to send ROK-manufactured weapons to Ukraine in its fight against Russia’s invasion. Most exhilarating to Taipei was Yoon’s April 2023 statement that the “Taiwan issue is not simply an issue between China and Taiwan but, like the issue of North Korea, [is] a global issue.” This was the first time an ROK president framed cross-Strait issues in global terms, and his words drew condemnation from the PRC Foreign Ministry. Yoon’s presidency also saw prominent ROK National Assembly lawmakers–including National Assembly Deputy Speaker Chung Woo-taik–visit Taiwan and hold meetings with prominent Taiwanese political figures, such as then-President Tsai Ing-wen (蔡英文).
From a strategic perspective, no ROK policy was more consequential to Taiwan’s security than Yoon’s pursuit of trilateral defense cooperation with the United States and Japan. Under the trilateral framework, Seoul engaged in an unprecedented set of defense and economic security activities with Tokyo and Washington, most prominently in the maritime field. The three countries’ armed forces conducted multiple naval exercises, including two “Freedom Edge” exercises in the East China Sea aimed at protecting “freedom for peace and stability in the Indo-Pacific.” Trilateral cooperation encouraged the sharing of intelligence as well as critical emerging technology.
Most notably, the framework aligned the ROK towards collaboration with two nations that have been historically more proactive on the subject of cross-Strait relations. Secondly, it accelerated trilateral cooperation on maritime security in East Asia, which is indelibly linked to the defense of the island nation of Taiwan.
Lee Jae-myung and the Democratic Party
The ROK’s left-leaning Democratic Party has never been as enthusiastic as Yoon’s PPP regarding the US-ROK alliance, ROK-Japan relations, and security cooperation against China. The DP’s leadership and voter base is dominated by the so-called “386 Generation”—that is, Koreans that were college-age during the late 1980s and participated in the protests calling for South Korea’s democratic transition. This generation is particularly aware of Washington’s historical support for South Korean dictators and is sympathetic towards the socialist ideals undergirding the ROK labor rights movement—another key force in the ROK’s democratization. The 386 Generation has been relatively supportive of reunification initiatives with North Korea—a policy for which Seoul has long relied upon the PRC for cooperation. For these reasons, the DP has advocated for a more balanced, or “independent,” position between the great powers of the PRC, Russia, and the United States.
Lee Jae-myung, however, is somewhat of an anomaly within the DP leadership. Unlike his counterparts—and previous DP presidents such as Moon Jae-in—Lee did not take part in the democracy protests of the 1980s. Lee was born to a poor working-class family and was forced to take factory jobs to support himself through his education—work that precluded participation in the heady student movements of the 1980s. Lee is regarded as a transactional politician with a populist bent, and lacks the socialist ideological convictions of his contemporaries in the Democratic Party. Indeed, Lee reportedly ordered provisions criticizing Yoon for “antagonizing” Russia and China stripped out of the December 2024 impeachment bill, undermining the views of the more progressive factions among the Korean left.
However, Lee has made several comments regarding ROK-Taiwan relations that indicate he would adopt more PRC-friendly policies than Yoon. In a 2024 campaign event in Chungcheong Province, he remarked that “Whatever happens in the Taiwan Strait, whatever happens in the domestic affairs of China and Taiwan, what does it matter to us?” His statement stood in stark contrast to Yoon’s position regarding the “global importance” of cross-Strait relations. Most striking was Lee’s decision to sit down alongside then-PRC Ambassador Xing Haiming at the Chinese Embassy in Seoul, while the latter publicly castigated Yoon’s security cooperation with Japan and the United States.
As a political figure with a reputation for populist policies over ideological fervor, it is difficult to judge whether Lee’s PRC-friendly rhetoric is intended to stir up the DP’s progressive base and differentiate himself from an unpopular incumbent, or whether they reflect Lee’s true intentions. In a February 2025 interview, Lee stated that on “the security front, [the ROK] needs US-ROK-Japan cooperation” and that the “US-ROK alliance is an extremely useful foundation for our economic development. We can’t throw out or interfere with that.” In the same interview, Lee promised to “place the national interest at the forefront and do what must be done.” With over 80 percent of South Koreans holding negative views of the PRC, it is entirely possible that, if elected president, Lee will react with policies more confrontational to the PRC than prior DP leaders.
However, given the constraints associated with his status as a DP politician, it is still worth considering what Taiwan and the United States can reasonably expect from Lee’s cross-Strait policies on the rhetorical and military fronts.
Rhetorical Support for Taiwan under Lee
When it comes to relations with great powers such as China, Democratic Party leaders—and indeed non-DP ROK presidents before Yoon–have tended to focus on practical outcomes over rhetorical positioning. For example, months after she had agreed to deploy the US-made Terminal High Altitude Air Defense (THAAD) system on South Korean soil despite relentless opposition from Beijing, former ROK conservative President Park Geun-hye met with Xi Jinping (習近平) in China and expressed a desire to “make bilateral relations even firmer through sincere communication.” Moon Jae-in, the last DP president, made his strongest statement on cross-Strait issues when a joint ROK-US declaration mentioned the importance of “preserving peace and stability across the Taiwan Strait.” Moon’s foreign minister Chung Eui-yong later clarified that the ROK’s position on cross-Strait issues had “not changed” and acknowledged the “unique relations between China and Taiwan.”
Though his weaker ideological convictions may not act as a check on Lee Jae-myung’s approach to ROK-Taiwan relations as president, his more transactional approach to policy making may encourage him to question what gains the ROK would make from pro-Taiwan rhetoric. Though Taipei has long relied upon cooperative statements from foreign countries as it seeks to promote a unified opposition to PRC aggression, words may not be the ROK’s wellspring of support for Taiwan under a presumed Lee Jae-myung Administration.
Defense Contributions to Taiwan under Lee
Trilateral Framework
Under a President Lee Jae-myung, a decline in trilateral cooperation between the ROK, the United States, and Japan may be the most consequential development for Taiwan’s security. Deeply aware of Japan’s colonial history in Korea, the ROK left wing holds on to net negative views of Tokyo. This is despite the fact that views regarding Japan among the general ROK public have trended positive since Yoon began his provocative pivot towards trilateral cooperation with Japan and the United States. Yoon’s unilateral overtures to Tokyo have caused consternation within the ideological wing of the Democratic Party. When the DP-led coalition of political parties first moved to impeach Yoon, progressive lawmakers included language criticizing Yoon’s “bizarre pro-Japan policies” and his “nomination of Japan-loving personnel to key government positions.” Again, Lee Jae-myung moved to strike this language out of the second impeachment bill, which ultimately passed.
Stuck between ROK citizens’ majority support for trilateral cooperation and the traditional opposition to Japan cooperation held by DP progressives, Lee is likely to take a middle ground. As Lee previously acknowledged, Seoul “needs US-ROK-Japan cooperation” and a Lee Administration would likely continue less-visible forms of trilateral engagement, such as intelligence sharing regarding North Korean missile launches. However, a Lee Administration is unlikely to immediately authorize joint naval exercises with the United States and Japan—measures that were so encouraging for Taipei’s fragile maritime security. Japan’s Maritime Self Defense Force is particularly provocative to the ROK left, in that it still flies a near-identical version of the Rising Sun Flag of the Empire of Japan. It may take years, and a drastically heightened threat from either the PRC or North Korea, for Lee to agree to joint naval exercises with Japan—if at all.
ROK-US Bilateral Cooperation
In contrast to their relationships with Japan, DP leaders have historically shown more willingness to collaborate on defense with Washington (even as some ROK progressives harbor resentment towards the United States’ cooperation with South Korean dictators). Even the most progressive DP presidents—such as Roh Moo-hyun—have deferred to US defense priorities. In 2003, former President Roh sent ROK troops to Iraq to support the US-led Operation Iraqi Freedom, eventually making South Korea the third-largest coalition partner behind the United States and the United Kingdom. Despite robust opposition from his base of support, Roh implemented the policy so as to enhance his administration’s relationship with the US government.
A President Lee Jae-myung could participate in US-led bilateral naval exercises aimed indirectly at the PRC, if Lee believes the cooperation will enhance his bargaining power in other bilateral negotiations with Washington–such as those related to diplomacy with North Korea. US President Donald Trump has revealed his desire to re-establish summit diplomacy with North Korea’s leader, Kim Jong-un. As a result, Lee may seek to barter bilateral defense cooperation on PRC issues for influence over the negotiations. However, the direction of US-ROK defense cooperation is more likely to be decided by emerging conflicts over bilateral trade deficits and South Korea’s expenditure on the US-ROK alliance. If Trump uses all his leverage on his objectives related to more equitable trade balances and greater ROK alliance spending, he might not have any cards left to pressure Lee into maritime cooperation against Beijing.
Image: Republic of Korea Navy vessels sail in a 2015 ceremony. (Image source: Wikimedia Commons)
ROK Unilateral Maritime Security Contributions
Instead of pressuring Seoul into maritime defense groupings vulnerable to domestic political headwinds, the United States—and its partner Taiwan—may find more success in backing the Democratic Party’s intrinsic interest in building a strong blue-water ROK navy. Partly as a consequence of historical trauma related to Korea’s powerlessness against invasions by the Japanese Empire and Qing Dynasty-era China, DP politicians have long advocated for a powerful blue-water navy to achieve a sense of security and autonomy. Perhaps surprisingly, DP administrations have raised defense spending by more than their conservative counterparts, and the party has approved expensive and controversial naval shipbuilding projects such as the CVX aircraft carrier. Indeed, among the few concrete military assets slated for acquisition in the DP’s manifesto for the 2022 presidential election (when Lee Jae-myung lost to Yoon Suk Yeol) were nuclear-powered submarines.
The ROK is deeply reliant on sea lines of communication (SLOCs) around Taiwan for its maritime trade, and is engaged in a maritime dispute with the PRC over control of Ieodo (also known as Socotra Rock) in the East China Sea. A DP-led construction of a larger ROK Navy is therefore likely to produce significant positive security externalities for Taiwan, in that the PRC may be forced to divert its navy away from incessant exercises around Taiwan in order to jockey with Seoul for control over the Yellow Sea. In so far as is politically possible, the United States should aid a potential Lee Jae-myung Administration’s advancement of a blue-water navy through measures such as technology transfer for nuclear-powered submarines. In doing so, Washington could support the growth of a new maritime counterbalance to the PRC in Northeast Asia, and a powerful force that could collaborate with democratic partners should ROK political winds turn again towards bilateral and trilateral cooperation.
The main point: An early ROK presidential election is forecasted to produce a victory for candidate Lee Jae-myung and his Democratic Party. Therefore, the United States and Taiwan should prepare for a Lee Administration that will likely be more reluctant to engage in overtly pro-Taiwan rhetoric. While Washington and Taipei should expect a Lee Administration to shy away from conspicuous trilateral defense cooperation with Japan and the United States, the Trump Administration can back the DP’s desire to establish the ROK’s own powerful blue-water navy that could distract the PRC navy from Taiwan, and allow Seoul to take greater responsibility for its sea lines of communication through the East China Sea.
