Earlier this month, U.S. President Donald Trump made high-profile visits to both Japan and South Korea as the first stops on his marathon twelve-day, five-country tour of East Asia. During his time in both Tokyo and Seoul, Trump largely stayed on script, stressing Washington’s longstanding commitment to the defense of both allies and his administration’s focus on building up robust deterrence and pressure to dissuade further provocations from North Korea, which has been rapidly enhancing its missile and nuclear capabilities over the past year. The promotion of trilateral security cooperation between Seoul, Washington, and Tokyo is hardly a new development, and has been prioritized by successive administrations over the past two decades.

One of the most vexing stumbling blocks to meaningful trilateral cooperation, however, has been the fraught relationship between South Korea and Japan, who remain at odds over a number of historical issues. Recent years provided some reason for cautious optimism and hopes for a thaw, thanks to a 2015 deal on the contentious issue of so-called “comfort women.” Buoyed by a tepid improvement on the political side, Japan and South Korea have also been moving forward on enhancing their bilateral defense and security cooperation. Key examples of this include the completion of a bilateral general security of military information (GSOMIA) agreement last year, and the agreement to establish a hotline between both defense ministers.

There have also been positive strides trilaterally, with a series of high-level meetings between diplomats and senior officials and a greater focus on synergizing efforts to deter North Korea. In addition, the two countries have demonstrated positive cooperation in the United Nations Security Council and elsewhere on imposing and implementing new sanctions against the Kim regime in North Korea. Seoul, Tokyo and Washington also have enhanced their trilateral intelligence sharing on Pyongyang’s weapons programs through the Trilateral Information Sharing Agreement, and they have noticeably stepped up the frequency of jointly planned exercises. Still, this military cooperation continues to be restrained due to Seoul’s concerns about Japan’s inclusion, as evidenced by the Blue House’s denial of Washington’s request to include Tokyo in a proposed trilateral exercise this month.

Despite the common strategic drivers to propel cooperation—both bilaterally and trilaterally with the United States—ties between Tokyo and Seoul remain uninspiring. No clearer example of this can be found than Trump’s recent visit to South Korea, when Moon invited him for a palatial state dinner to discuss the importance of the Washington-Seoul relationship. While the dinner should have provided an opportune occasion to reinforce the alliance, show solidarity in the face of growing aggression from North Korea, and indicate unity with Japan’s security, it instead turned into a sideshow given Moon’s decision to invite one of the remaining living “comfort women” to attend the ceremony. The political pettiness was magnified by the childish decision to serve “Dokdo shrimp,” allegedly from the waters surrounding the disputed Liancourt Rocks (claimed by both South Korea and Japan) in the Sea of Japan. South Korea administers the islets and refers to them as Dokdo, while Japan calls the rocks Takeshima and claims they belong to its Shimane prefecture.

Why would Moon make such a provocative move? First, South Korea constantly pushes for greater attention to the history issue from the United States, which has traditionally—and understandably—been reluctant to take sides between its two East Asian allies. Moon’s thinly veiled symbolism at the dinner, however, was not aimed at impressing Trump or impacting Washington’s position on the lingering historical disputes between Tokyo and Seoul. Rather, the driver was domestic politics, and Moon’s desire for an easy win by taking digs at Japan. Such moves are usually welcome among the South Korean public, which is largely critical of Tokyo and the conservative Abe Administration, especially on issues related to Dokdo/Takeshima and the “comfort women.”

Moon’s position on Japan also continues to raise eyebrows in Tokyo. There could be rocky times ahead on a number of key bilateral issues, including the maintenance of the 2015 comfort women deal, which Moon has publicly derided as insufficient. In response to this, Abe thus far appears to be cautiously waiting out Moon and will look to focus initial talks and cooperation on the one area where there is a semblance of agreement—preventing new provocations from North Korea.

Another key factor for Tokyo and Seoul’s ties is the trajectory of U.S.-South Korea relations. Analysts are cautious and uncertain about the future of the Moon-Trump relationship, which is now under stress over plans to renegotiate the U.S.-Korea Free Trade Agreement. There is also concern about how Washington’s “Maximum Pressure and Engagement” strategy dovetails with Moon’s desire to retro-fit Seoul’s hardened approach to the North. In some sense, at least, there could be common ground between the two: both have signaled engagement is a possibility, including even meeting with leadership in Pyongyang.

That said, there are also glaring divergences apparent in the U.S.-South Korea relationship, which could sour ties in the near future. Moon seems disenchanted with the “deterrence plus” approach of turning the screws on North Korea, and will likely resist calls for talks on more robust trilateral security cooperation with Japan. Moon is also likely to brush off recommendations of enhanced regional missile defense. He has previously bristled at the now-installed Terminal High Altitude Area Defense (THAAD) missile defense battery and the Japan-South Korea GSOMIA intelligence-sharing pact.

Initial indications have stoked skepticism in Tokyo on how Moon may look to engage with Japan. Adding to these complexities is the thaw between China and South Korea, who recently agreed to downplay their public feud over the deployment of THAAD on the Korean peninsula. Beijing will no doubt use this renewed political space with South Korea to pry away at the U.S.-Japan-South Korea trilateral relationship, a long-held goal for China.

Despite these ominous signs, though, it is important to recognize that Moon was not elected on foreign policy issues—or his policy on Japan more specifically—but rather on his economic policies and his seizure of the electoral space in the wake of Park Geun-hye’s impeachment. Second, Moon is likely to be hemmed in, to some extent, on his new designs for foreign policy by the opposition parties in the National Assembly and also by regional provocations from the North. These structural factors will hopefully push Moon to pragmatism in ties with Tokyo over the coming months.

The alternative path, which remains a possibility, would be an increasingly nationalist and uncompromising approach from the Moon Administration with regard to its bilateral relations with Japan. This road would all but ensure that Japan and South Korea continue to be mired in an antagonistic cycle of action and reaction, making no real attempt to mitigate risks to the relationship. In this scenario, tensions would become semi-permanent and all-encompassing rather than intermittent and manageable through adept diplomacy. The Trump Administration should pay attention to these developments and be sensitive to these tensions while pushing for reconciliation and deeper political exchanges, especially on issues beyond North Korea.