President Joe Biden is devoting his Saturday to cementing ties with South Korea and its new leader Yoon Suk Yeol as the two sides consult on how best to check the nuclear threat from North Korea at a time when there’s little hope of real diplomacy on the matter.

The division of the Korean peninsula after World War II has led to two radically different nations. In South Korea, Biden is touring factories for computer chips and next-generation autos in a democracy and engaging in talks for greater cooperation. But in the North, there is a deadly coronavirus outbreak in a largely unvaccinated autocracy that can best command the world’s attention by flexing its nuclear capabilities.

Speaking to reporters aboard Air Force One as Biden made his way to South Korea, White House national security adviser Jake Sullivan said the U.S. has coordinated with Seoul and Tokyo on how they’ll respond should the North conduct a nuclear test or missile strike while Biden is in the region or soon after. Sullivan also spoke with his Chinese counterpart Yang Jiechi earlier in the week and urged Beijing to use its influence to persuade the North to cease the tests.

“China should contemplate taking whatever steps it can to reduce the possibility of a provocative” act, Sullivan said.

As part of a five-day visit in Asia, Biden is focusing his Saturday on his relationship with Yoon, who assumed office little more than a week ago. One mission will be reassuring South Korea about the U.S. commitment to countering North Korea‘s Kim Jong Un.

Also Read: Is China’s zero COVID strategy failing?

There’s worry in Seoul that Washington is slipping back to the Obama administration’s “strategic patience” policy of ignoring North Korea until it demonstrates seriousness about denuclearization, an approach that was criticized for neglecting the North as it made huge strides in building its nuclear arsenal.

Prospects for real nuclear diplomacy are slim as North Korea has ignored South Korean and U.S. offers of assistance with its COVID-19 outbreak, dimming hopes that such cooperation could help ease nuclear tensions or even lead to talks. Still, Biden and Yoon are expected to discuss ways to work with the international community to get the North much needed vaccines and tests, according to senior Biden administration officials who briefed reporters.

The U.S. president plans to lay a wreath at the country’s national cemetery, meet privately with Yoon, hold a joint news conference and then attend a state dinner at the National Museum of Korea.

One focus is sure to be a North that is menacing yet economically fragile. Yet both leaders also are keen to emphasize their growing trade relationship as two Korean industrial stalwarts — Samsung and Hyundai — are opening major plants in the U.S.

Biden faces growing disapproval within the U.S. over inflation near a 40-year high, but his administration sees one clear economic win in the contest with China. Bloomberg Economics Analysis estimates that the U.S. economy will grow faster this year than China for the first time since 1976, a forecast that White House press secretary Karine Jean-Pierre credited to Biden’s spending on coronavirus relief and infrastructure that led to faster job growth.

The national security event that is galvanizing broader discussions between the two countries has been Russia’s invasion of Ukraine, a war that has led to an unprecedented set of sanctions by the U.S. and its allies.

South Korea joined the U.S. in imposing export controls against Russia and blocking Russian banks from the SWIFT payments system. Its participation was key to stopping Russia’s access to computer chips and other technologies needed for weapons and economic development.

At the start of the administration, many White House officials thought that Kim’s nuclear ambitions would prove to be perhaps the administration’s most vexing challenge and that the North Korean leader would aim to test Biden’s mettle early in his time in office.

Through the first 14 months of Biden’s administration, Pyongyang held off on missile tests even as it ignored efforts by the administration to reach out through back channels in hopes of restarting talks that could lead to the North’s denuclearization in return for sanctions relief.

But the quiet didn’t last. North Korea has tested missiles 16 separate times this year, including in March, when its first flight of an intercontinental ballistic missile since 2017 demonstrated a potential range including the entire U.S. mainland.

The Biden administration is calling on China to restrain North Korea from engaging in any missile or nuclear tests. Speaking on Air Force One, Sullivan said Biden and Chinese President Xi Jinping could hold a phone call in the coming weeks.

Biden has fiercely criticized Beijing over its human rights record, trade practices, military harassment of the self-ruled island of Taiwan and more. And while Biden has made clear that he sees China as the United States’ greatest economic and national security competitor, he says it is crucial to keep the lines of communication open so the two powers can cooperate on issues of mutual concern. North Korea is perhaps highest on that list.

White House officials said Biden won’t visit the Demilitarized Zone dividing the Korean peninsula during his trip — something that’s become standard for presidents during Seoul visits dating back to Ronald Reagan. Biden visited the DMZ in 2013 as vice president. Sullivan said the president’s decision to skip the stop this time wasn’t driven by security concerns.

Instead, Biden on Sunday will visit the Air Operations Center’s Combat Operations Floor on Osan Air Base, south of Seoul. The U.S. sees it as one of the most critical installations in Northeast Asia.