SEOUL – President Moon Jae-in of South Korea has a message for the United States: President Biden must now deal with North Korea.

In an interview with the New York Times, Mr. Moon urged the American leader to start negotiations with the government of Kim Jong-un, the leader of North Korea, after two years of stalling diplomatic progress were even reversed . Denuclearization is a “question of survival” for his country, said the South Korean president.

He also called on the United States to work with China on North Korea and other issues of global concern, including climate change. The deteriorating relations between the superpowers could undermine any negotiations on denuclearization.

“If tensions between the United States and China intensify, North Korea can benefit and capitalize on it,” said Moon.

It was partly a plea, partly a sales pitch, from Mr. Moon, who sat down with The Times as the United States tried to rebuild ties in the region to counter China’s influence and North Korea built its nuclear arsenal. Mr. Moon, who will meet Mr. Biden in Washington next month, seemed ready to take on the role of mediator between the two sides again.

Interviewed, Mr. Moon prided himself on his skillful diplomatic maneuvering in 2018 as he led the two unpredictable leaders of North Korea and the United States for a face-to-face meeting. He was also pragmatic, tacitly admitting that his work to achieve denuclearization and peace in the Korean Peninsula has since disintegrated.

President Donald J. Trump stepped down without removing a single North Korean nuclear warhead. Mr. Kim has resumed weapon testing. .

“He beat the bush and didn’t manage to pull it off,” said Mr. Moon of Mr. Trump’s efforts on North Korea. “The most important starting point for both governments is to have the will to dialogue and to meet face to face early on.”

Now, in his final year in office, Mr. Moon is determined to start over – knowing that in Mr. Biden he is facing a very different leader.

Mr. Moon relied on Mr. Trump’s style and emphasized the personality-driven “top-down diplomacy” through one-on-one interviews with Mr. Kim. Mr Biden, he said, is going back to the traditional “bottom-up” approach, where negotiators haggle over details before getting approval from their bosses.

“I hope that Biden will go down as a historic president who has made substantial and irreversible progress towards full denuclearization and peace settlement on the Korean Peninsula,” Moon said in an interview with Sangchunjae, a traditional hanok on the grounds of the Executive Residence, Blue House.

Mr. Moon’s visit to Washington comes at a crucial time. The Biden administration completes its month-long policy review regarding North Korea, one of the most pressing geopolitical issues facing the United States.

Mr Biden has begun to reverse many of his predecessor’s foreign policy decisions. But Mr Moon warned that it would be a mistake to kill the 2018 Singapore Accord between Mr Trump and Mr Kim, which set broad goals for the denuclearization of the Korean Peninsula. .

“I believe if we build on what President Trump has left, we will make these efforts a reality under Biden’s leadership,” he said.

Mr. Moon urged the United States and North Korea to take “incremental and gradual” steps towards denuclearization, while “at the same time” exchanging concessions and incentives. It was a well-worn script for Mr. Moon who occasionally paused during the interview to refer to his notes and underscored his speech with small but determined hand gestures.

Some past American negotiators and Mr. Moon’s conservative critics oppose such a strategy, saying North Korea would stall and undermine international sanctions, the best leverage Washington has on the impoverished country. In his annual threat assessment released last week, the director of national intelligence for the United States said that Mr. Kim “believes that over time he will gain international acceptance and respect as a nuclear power.”

However, Mr. Moon’s team argues that the step-by-step approach is the most realistic, even if it is not perfect. According to his administration, North Korea would never give up its arsenal in a single step lest the regime lose its only negotiating chip with Washington.

The key, Mr. Moon said, is that the United States and North Korea work out a “mutually trustworthy roadmap.”

American negotiators under Mr. Trump never made it to this point. Both sides could not even agree on a first step for the north and what reward Washington would get for doing so.

Mr. Moon is not only trying to save his “Korean Peninsula Peace Process”, but also arguably his greatest diplomatic legacy.

When his North Korea policy stalled, critics called him a naive pacifist who relied too much on Mr Kim’s unproven commitment to denuclearization.

“His good intentions had dire consequences,” said Kim Sung-han, a professor at Korea University. “His mediation has not worked, nor have we made any progress on denuclearization. His time is running out. “

Since negotiations stalled, Mr. Moon’s problems at home have increased. Its approval ratings have fallen to hit lows amid real estate and other scandals. This month, angry voters brought his Democratic Party devastating defeats in the mayoral elections in South Korea’s two largest cities.

This is a sharp turn from the start of his term in office when Mr. Moon turned a hair-raising geopolitical crisis into a political initiative.

“When I took office in 2017, we were very concerned about the possibility of another outbreak of war on the Korean peninsula,” he said.

Four days after his tenure, North Korea launched its medium-range ballistic missile Hwasong-12, which could attack Hawaii and Alaska. Then the north tested a hydrogen bomb and three ICBMs. In response, Mr. Trump threatened “fire and anger” when carrier groups from the American Navy steamed onto the peninsula.

Mr. Moon’s first diplomatic victory came when Mr. Kim accepted his invitation to send a delegation to the 2018 Winter Olympics in Pyeongchang, South Korea. Shortly afterwards, Mr. Moon met with Mr. Kim at the heavily armed inter-Korean border.

During that meeting, Mr. Moon said the North Korean dictator had hinted that disarmament was a real possibility. “If security can be guaranteed without nuclear weapons, why should I have difficulty holding them at the expense of sanctions?” Mr. Moon remembered Mr. Kim.

He said he pitched Mr. Trump and asked him to meet Mr. Kim. At their television summit in Singapore, Trump promised “security guarantees” for North Korea, while Mr. Kim pledged to “work towards a full denuclearization of the Korean peninsula”.

“It is clearly an achievement for President Trump to hold the first North Korea-United States summit,” he said.

But Mr. Moon also lamented that Mr. Trump never got through after declaring that “there is no longer a nuclear threat from North Korea”. When Mr Kim and Mr Trump met again in Hanoi, Vietnam, in 2019, negotiations were going nowhere and the men left without reaching an agreement on how to move forward with the Singapore deal.

While Mr. Moon was keen to praise Mr. Trump, he also appeared frustrated with the former president’s erratic behavior and Twitter diplomacy. Mr. Trump canceled or downsized the annual joint military exercises the United States conducts with the South, demanding an “excessive amount” to keep 28,500 American troops in South Korea.

Mr Moon said he had decided to suspend negotiations on the so-called defense cost sharing agreement during Mr Trump’s final months in office. South Korea was willing to pay more given its growing economic size, but Mr Trump’s demands went against the very foundation of the two countries’ relations.

“His request lacked a reasonable and rational calculation,” said Moon.

The fact that Washington and Seoul could strike a deal within 46 days of Mr Biden’s inauguration is “clear evidence of the importance President Biden attaches to the alliance.”

Mr. Moon is confident of the progress the new American leader can make in North Korea, although a major breakthrough may be unrealistic given the deep distrust between Washington and Pyongyang.

Mr Biden said last month that he was “prepared for some form of diplomacy” with North Korea, but that “it must be made contingent on the end result of denuclearization”.

North Korea has come up with ideas for a step-by-step approach that begins with the demolition of its only known nuclear test site, followed by the dismantling of a rocket engine test facility and the nuclear complex in Yongbyon north of Pyongyang.

Mr Moon said he believes such steps, when combined with American concessions, could result in the removal of the North’s more valuable assets such as ICBMs. In this scenario, the step towards complete denuclearization becomes “irreversible”.

“This dialogue and this diplomacy can lead to denuclearization,” he said. “If both sides learn from the failure in Hanoi and put their heads together on more realistic ideas, I am confident that they can find a solution.”