President Moon Jae-in’s “balanced diplomacy” will be put to the test at the South Korea-US summit on Tuesday.

In an interview Friday with Channel NewsAsia, a Singaporean cable television news agency, Moon said, “The relationship with China has become more important not only in terms of economic cooperation, but also for strategic cooperation for the peaceful resolution of the North Korean nuclear issue. That is why I am pursuing a balanced diplomacy with the US as well as China.”

The key point of his balanced diplomacy approach lies in securing cooperation from China on North Korea issues while maintaining the alliance with the US. It gained momentum from the Seoul-Beijing agreement last week to mend their ties over the deployment of a US antimissile system.

The problem is, if relations between Washington and Beijing are strained and confrontational, South Korea will find it difficult to perform a balancing act between them.

This balanced diplomacy can work only when US-China ties are cooperative and South Korea are trusted by the two countries.

South Korea may look opportunistic and untrustworthy in the eyes of both powers and be passed over. Such a possibility will arise when Washington and Beijing are engaged in hegemonic rivalry.

The liberal administration of former President Roh Moo-hyun tried a balanced diplomacy only to drop it amid a negative response from the US.

Former President Park Geun-hye also attempted a diplomacy to align South Korea’s relations with the US and China, but eventually it ran aground over China’s opposition to Seoul’s decision to host the Terminal High Altitude Area Defense system.

Latitude for Moon to try a balanced diplomacy will be swayed by how the US-China summit turns out. At present, the two countries are seen as moving toward cooperation over North Korean threats, opening some space for balancing acts between Washington and Beijing. But the Moon administration must keep in mind that its security diplomacy should be based on its alliance with the US. South Korea should make it a rule to expand its cooperation with China on the foundation of its relations with the US.

Moon needs to convince US President Donald Trump in their summit meeting that there will be no change at all to this principle.

Efforts to strengthen cooperation with China are desirable in solving the North Korean problem. A balanced diplomacy is worthwhile as long as it serves the security interests of the US, China and South Korea at the same time and also if it does not damage Korea-US ties.

In a parliamentary audit on Oct. 30, Foreign Minister Kang Kyung-wha disclosed three government positions for better relations with China. The government will not consider hosting additional THAAD systems, nor join the US missile defense network. Nor will it form a three-nation military alliance with the US and Japan.

The positions have caused concern that South Korea conceded too much to China in order to restore their relations or that the Moon administration stepped away from the US to get closer to China.

Although the presidential office said it had consulted Washington and secured its understanding on the three positions beforehand, concern has not been assuaged.

In a roundtable interview with news media from the five Asian nations that Trump will visit, US National Security Adviser H.R. McMaster said he did not “think that South Korea would give up its sovereignty in those three areas.” This amounts to a warning not to detract from the alliance with the US.

Moon’s balanced diplomacy is sustainable only when both the US and China trust its neutrality. If either side loses trust in South Korea, the diplomacy will lose its footing.

That is why walking on a diplomatic tightrope is risky. Once trust is lost, it will take a long time to restore it.

If Trump raises an issue of the positions, Moon needs to convince him that his balanced diplomacy will help defuse North Korean threats through cooperation with Beijing.