The upcoming summit talks between President Moon Jae-in and US President Donald Trump pose challenges for both leaders that are incomparable to those faced by their recent predecessors.

Moon and Trump have many sensitive and complicated issues to tackle, casting uncertainty over their first meeting.

Amid North Korea’s nuclear and missile threats, the two leaders first have to deal with the controversial deployment of a US anti-missile system in South Korea. More broadly, Moon and Trump need to reach an agreement on how to curb the North’s security threat.

Economic issues, such as the possible renegotiation of the Korea-US free trade agreement, will also be high on the agenda for the Moon-Trump talks set for June 29-30 in Washington.

What makes the talks more complicated is that both Moon and Trump are different from their predecessors in many respects. Moon is the first liberal Korean president in nine years and he is largely expected to seek a change in the South Korean policy toward the US.

By now, the world knows well how different Trump is from past US leaders and how unpredictable he is.

His “America First” approach is a big cause for concern for South Korea, too. He has already called for the renegotiation of the Korea-US free trade agreement and more payment from Korea for American forces stationed here, among other things. He even once suggested that Seoul pay for the cost of the US missile defense system being installed in Seongju, North Gyeongsang Province.

In light of all these factors, one cannot help but be more concerned than hopeful over the upcoming talks in Washington.

But the current situation does not leave room for the two leaders to go their own way – just consider the urgent need to jointly cope with the growing threat from North Korea’s nuclear and missile development, which even stoked fears of war on the peninsula a while ago.

The most pressing issue Moon and Trump should tackle -- and reach an agreement on -- is the deployment of the Terminal High Altitude Area Defense system.

The issue has become more complex in recent weeks, with some US politicians and media suspecting that the Moon administration may eventually withdraw the decision to deploy the THAAD battery aimed to counter North Korean missiles.

To be fair, there are grounds for the US to take a skeptical view of the position of the new South Korean government.

Whether he intended to or not, Moon’s order to probe the allegation that the Defense Ministry kept him in the dark about the arrival of additional launchers for the THAAD battery bolstered the position of South Koreans who oppose the US missile shield system. Moon’s order to assess its environmental impact -- which could take up to one year -- also officially suspended its deployment.

Moon needs to convince Trump in Washington that the Seoul government will not revoke the decision to host the US anti-missile system. Pledging to complete the environmental survey as soon as possible and offering a clear timetable for setting the THAAD battery into operation could be two ways.

In addition, Moon and Trump should fine-tune their policy toward North Korea. It is no exaggeration to say that Trump’s North Korea policy has been unclear, ranging from talk of a pre-emptive strike against the North’s key facilities to a hint at talks.

For his part, Moon has been preaching the need to appease the Pyongyang government, raising concerns that some of his peace overtures -- such as the possible reopening of South Korean-run factories in a North Korean city -- could interfere with UN-led international sanctions imposed as punitive measures over the North’s nuclear and missile provocations.

The Washington meeting should set a clear direction for the two allies’ future approach toward the North, especially regarding sanctions and diplomatic negotiations.

What is clear is that the two countries cannot afford any crack in their decadeslong alliance and partnership, which not only benefit them but also play a crucial role in preserving peace in the region. Moon, Trump and officials working for the Washington summit should bear that in mind.