Kim Ki-jung, the second vice chief of the National Security Office, who was regarded as a mentor to President Moon Jae-in on foreign affairs and national security, offered to resign Monday.

Yoon Young-chan, senior presidential secretary for public relations, said Kim felt a “moral responsibility” to step down. According to some news reports, the presidential office practically sacked him for “inappropriate conduct” at Yonsei University when he was a professor there. Many tip-offs and complaints against him reportedly came in to Cheong Wa Dae after he was appointed.

The immediate problem is preparation for Korea-US summit this month.

The second vice chief of the NSO takes charge of foreign affairs, national unification and security issues. Secretaries to the second vice chief have not been appointed yet. Working-level preparations for the summit cannot but hit a snag.

Kim had served Moon as an adviser on foreign affairs and national security since 2012, and his resignation has left a big hole in the security policy framework of the new administration. Cheong Wa Dae has come back to square one in its attempt to form its foreign policy and security team.

Worse still, Kang Kyung-wha faces dim prospects of being confirmed as foreign minister. She is suspected of false address registration and tax evasion. She also has no experience in the field of national security.

If it becomes difficult to name her as a Cabinet member, Moon may have to go to the US without a foreign minister. If the appointments of foreign minister and the NSO second vice chief are drawn out, preparations for the G20 summit in Germany early next month will also face difficulties.

Moon needs to name Kim’s successor as soon as possible and staff up his team. However, a loose vetting process will take Cheong Wa Dae back to where it came in. The presidential office should try its best to vet candidates for positions related to security.

Cheong Wa Dae would find it hard to refute criticism over its vetting of Kim and Kang. It could have detected Kim’s problematic behavior by asking his acquaintances about his reputation. Details on Kang’s false address registration may have been found if a copy of her residence registration had been checked carefully.

Moon kept Lim Sung-nam as first vice minister of foreign affairs on Tuesday. The decision came a bit late but was a right and necessary thing to do, considering the coming summit with US President Donald Trump. The first vice foreign minister is in charge of bilateral relations with the US and other countries.

The Moon administration seems to have gotten off to a rocky start in the area of foreign policy and security. It is questionable whether Chung Eui-yong, chief of the NSO, and Lee Sang-chul, first vice chief of the office, made the right response to the Defense Ministry’s omission of Terminal High Altitude Aerial Defense launchers in its briefing. Some accuse them of kicking up an unnecessary fuss.

Normally, major agenda items are coordinated before the opening of a summit. Moon will fly to Washington for his first talk with Trump in a few weeks. The meeting will set the tone of the US-Korea relations for at least four years.

As everybody knows, Trump, a former businessman, is hard to predict. So, a thorough preparation is needed more than ever before.

Adding to these worries is the current atmosphere between Seoul and Washington over the THAAD issue. Moon ordered the investigation of the Defense Ministry’s decision on the environmental impact assessment of the system. Chung told his White House counterpart H.R. McMaster its environmental impact should be thoroughly assessed. The system may not be fully deployed this year.

If the THAAD problem sours their relationship, the negative effect on South Korea’s national security may last for a long time.