Kenji Yoshida 
(©Lee Jae-myung Facebook page.)
Lee Jae-myung, leader of South Korea's main opposition Democratic Party, is swiftly emerging to fill the vacuum left by President Yoon Suk-yeol's abrupt ouster.
On April 4, the Constitutional Court unanimously ruled to remove Yoon from office, citing his controversial declaration of martial law.
Lee's ascent is already in full throttle. On Sunday, April 20, he secured a second decisive victory in the DP's primary. Recent polls show him outpacing top contenders from the ruling People Power Party in hypothetical head-to-head matchups.
Barring any major shift in public sentiment or an unexpected alliance among his rivals, Lee appears well-positioned for the June 3 presidential race.
Such a prospect, however, is rattling policymakers in Japan and the United States.
Since taking office, Yoon has made revitalizing ties with Tokyo and Washington a cornerstone of his foreign policy. Those efforts culminated in two landmark agreements: the Camp David Accords and the Washington Declaration in 2023.
But all of this now hangs in the balance, as a staunchly left-leaning — arguably anti-Japan and anti-American — candidate leads in the polls.
Unrelenting Japan-bashing
From the outset, Lee has lambasted Yoon's Japan policy as one of "humiliation and subservience."
He fiercely opposed the Yoon administration's third-party compensation plan for wartime labor victims — a workaround meant to resolve tensions stemming from the preceding Moon Jae In era.
In August 2023, amid Tokyo's release of treated water from the Fukushima nuclear plant, Lee escalated his rhetoric, likening the move to a "second Pacific War."
Lee has openly called for scrapping the wartime compensation scheme and has questioned the safety of Fukushima water release on several occasions.
Ruriko Kubota, a veteran journalist from The Sankei Shimbun, warned that Lee could reignite long-dormant historical disputes if elected. "We may see the wartime labor and other sensitive issues like the comfort women flare up again," she said.
While Lee appears to have dialed down incendiary language, Kubota argues it's a calculated election strategy to sway undecided centrist voters.
"For Lee, South Korea's establishment is synonymous with pro-Japanese collaboration," she said. "He's weaponized that resentment, turning anti-Japan sentiment into a driving force behind his political rise."
"Animosity toward Japan runs deep, and it's dangerous to assume he's truly abandoned that position," Kubota added, cautioning against reading too much into his recent tone.
Resisting Deeper Military Ties
Lee's long-standing animosity toward Japan has naturally extended into the regional security realm.
In August 2023, for instance, while opposing deeper trilateral military cooperation with Tokyo and Washington, he said, "There can be no blind military cooperation with a Japan that shows not the slightest remorse for its past."
His remarks notably came just days before the Camp David summit.
Even with escalating regional security concerns, the firebrand has branded Yoon's attempt to deepen security ties with Japan as an extreme pro-Japan policy.
Such views are deeply embedded in his political record. In 2016, while serving as mayor of Seongnam, Lee described Japan as a "military adversary" capable of threatening South Korea's national security.
Lee's steadfast resistance is rooted in two main reasons. First, he sees Japan's deeper military involvement as a gateway to remilitarization reminiscent of its imperial past — one that could ultimately threaten the contested territory of Takeshima [Dokdo].
The other stems from his insistence that security cannot be separated from unresolved historical grievances. Lee has repeatedly argued that meaningful military coordination with Japan must be "preceded by a reckoning with the past."
Washington Watches Warily
Japan is not alone in its unease over Lee Jae-myung's ascent. Across the Pacific, American lawmakers and experts have voiced similar apprehensions.
In a January 17 interview with the Chosun Ilbo, US Representative Young Kim said, "If the factions behind the impeachment in South Korea continue to steer the current situation, North Korea and China will seize this opportunity to weaken the US–South Korea alliance."
Her remarks reflect growing concerns in Washington that Seoul's posture could shift dramatically under a left-wing leadership.
A recent vote in the National Assembly offered a glimpse of that trajectory. On March 13, 23 opposition lawmakers abstained, while 17 voted against a bill to strengthen military cooperation with the US.
Ironically, most dissenters belonged to Lee's party — the same party that had introduced the resolution.
Lee and his party's affinity for Beijing also raises red flags in the Trump circle, where containing China remains a core pillar of its diplomatic strategy.
CAPTION: Opposition leader Lee Jae-myung meets with then-Chinese Ambassador to South Korea Xing Haiming, June 8, 2023 (©DP Facebook)
"From everything we've seen, Lee wants to take South Korea down a path of aligning with Beijing and drifting closer to socialism," said Gordon Chang, an American attorney and China expert. "If South Korea were to fall under a pro-communist regime, it would severely undermine President Trump's Indo-Pacific strategy."
Beyond defense, Washington sees South Korea's leftward drift complicating collaboration in critical sectors such as civilian nuclear energy, shipbuilding, and economic security.
Can the Trilateral Pact Survive?
While fears of unraveling hard-won détente between Seoul and Tokyo are warranted, some argue the current dynamics are more nuanced than the Moon era.
"Political approaches rooted in anti-Japan rhetoric are losing their effectiveness," said Masatoshi Muto, former Japanese Ambassador to South Korea.
"South Koreans are, by and large, becoming more favorable toward Japan, while Japanese interest in Korean culture, cuisine, and society continues to grow," he added. "The challenge now is how to cultivate this positive momentum."
Other factors point to a more cautious but optimistic outlook. anti-Japan sentiment has been replaced by increasing anti-China sentiment.
Japan Press Research Institute reported in a 2024 survey that 44% of South Koreans viewed Japan positively, marking a record high for the second consecutive year. Meanwhile, negative perceptions of China have surged, especially among the younger generation.
Much of the previous frictions, moreover, stemmed from the personal dynamics at the top. Prime Minister Shinzo Abe and President Moon's relationship was defined by mutual distrust, with both leaders often benefiting domestically from their hardline policies. That tension-filled dynamic no longer exists.
And so long as Seoul's cozy relationship with Tokyo remains intact, any serious recalibration with Washington remains unlikely.
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Author: Kenji Yoshida
