Yet while meeting with visiting US Senator Dick Durbin on May 31, Moon said his order for an investigation into the clandestine transportation is "purely a domestic measure", not about "trying to change the existing decision or sending a message to the United States".
The mixed signals came at a time when China and the ROK, whose relations suffered a blow because of Seoul's decision to allow the deployment of THAAD, seem ready to move on to make up for lost time.
President Xi Jinping was among the first state leaders to congratulate Moon on his election victory. The new ROK president, apart from pledging on the presidential campaign that he would review the decision of his predecessor, the impeached and ousted Park Geun-hye, to deploy THAAD, also sent representatives and special envoys to attend the Belt and Road Forum for International Cooperation in Beijing last month.
But the continuing deployment of THAAD remains a thorn in bilateral ties. It is understandable that Moon is cautious about stalling the rollout of THAAD, because it may thwart his party's efforts to win more seats in the National Assembly and complicate US-ROK relations. Besides, he is due to visit the US later this month, his first state visit since assuming power.
But Moon will find it very difficult to appease both Washington and those opposed to THAAD's deployment－many ROK citizens and regional players such as China and Russia. During Moon's campaign trail, many of his supporters hoped that, if elected president, he would stall THAAD.
That news of four more THAAD launchers transported to the ROK failed to reach Moon in advance highlights the disparities between the president and the conservatives, as well as the fact that the deployment serves only a few interest groups, not the ROK's national interest.
China-ROK relations will see limited improvement if Seoul decides to accommodate and activate THAAD. The anti-missile system poses a serious threat to China's security and strategic interests, and the Chinese government has every reason to protest against its deployment. Paying lip service to the good-neighborly relations will not convince Beijing of the "urgency" of deploying THAAD.
More importantly, the continued deployment of THAAD could thwart global efforts to resolve the Korean Peninsula nuclear issue. Moon has advocated a constructive approach to the reconciliation with the Democratic People's Republic of Korea. But his DPRK policy can only succeed when all involved parties are on the same page, and Seoul's inclination to allow the rollout of THAAD could also sour Beijing-Washington ties.
The delay in the rollout could be an opportunity for the Moon administration to double check the procedural legitimacy and notify ROK citizens of THAAD's undesirable side effects. US President Donald Trump, who has more than once expressed willingness to cooperate with China on critical issues, could show his sincerity by making a right decision on THAAD.
The author is a researcher in Asia-Pacific strategy at the Chinese Academy of Social Sciences.
