The United States is about to deploy its diplomatic and military heft to the Korean peninsula to re-set relations after fours years of Donald Trump’s highly unusual approach to the region.

Although meetings with North Korea’s leader Kim Jong Un do not form part of the itinerary, his metaphorical shadow looms large over the trip as the Americans and South Koreans discuss how to get him back to the negotiating table.

Mr Kim is the third in his family to hold the title of Supreme Leader of North Korea and, at just 37 years old, he could potentially rule for several more decades.

But some experts believe his preference for expensive champagne, imported cheese, Russian vodka and cigarettes are the greatest threat to the Kim Jong Un dynasty.

Bong Young-shik, a research fellow at Yonsei University Institute for North Korean Studies, said Mr Kim’s health has been questionable right from the start.

“When he assumed power at the age of 27, about 10 years ago, he was already overweight,” he said.

While the size of someone’s body does not necessarily indicate poor health, there have long been rumours that Mr Kim has suffered from gout and other maladies.

“He showed a problem with the breathing when he was walking to greet South Korean President Moon Jae-in their first time in meeting in 2018,” Mr Bong said.

Although Donald Trump’s in-person meetings with the reclusive dictator were criticised for gifting him a PR victory without any concrete moves on denuclearisation, one of the benefits was allowing South Korean and American security forces to get a closer look at Kim Jon Un.

Bong Young-shik said it was not a kind assessment.

Then Kim Jong Un went missing for a while

Throughout 2020 there were multiple occasions when Kim Jong Un’s lack of public appearances led to speculation that he was close to death, or had already died.

Bong Yong-shik said although there is no current sign of an illness, Kim Jong Un’s health is a live issue.

“His health is closely watched, not [just] by the outsiders, but also North Koreans,” he said.

“The concern [is] of a sudden power vacuum or leadership collapse inside North Korea.”

Tae Young Ho is a former North Korean diplomat who fled his home country for the south and is now a legislator in the South Korean Assembly.

Although he said it is difficult to get accurate information about the health of the leader, the regime’s reaction to the COVID-19 pandemic illustrates the lack of confidence in the medical system.

“Kim Jong Un knows very well that there is no health infrastructure in North Korea to cope,” Mr Tae said.

“That’s why they totally blocked off North Korea. They stopped all the movements of North Korean people from cities to other cities.

“So that is the North Korean way of quarantine, and I think Kim Jong Un made some success in this regard.”

Who takes over if a new leader is suddenly needed?

In addition to speculation over Kim Jong Un’s health, in 2020 there was increasing focus on Kim Jong Un’s younger sister Kim Yo Jong.

Tae Young Ho describes Kim Yo Jong as “highly intelligent” and with a tight bond with her brother forged during childhood.

Both were hidden away, not acknowledged as the children of their father and mostly isolated from other children.

“That’s why the solidarity between Kim Jong Un and Kim Yo Jong is very strong, they usually [do] not believe in the people around them,” he said.

“That’s why there are successive changes of leaders of North Korean systems.”

The elevation of Kim Yo Jong to a more high-profile position may have been in reaction to the US assassination of Qassem Soleimani, an Iranian major general last year.

The US managed to kill the well-protected major general through a targeted drone attack.

“America showed a kind of technology that they can kill anyone from tens of thousands of kilometres’ away with the computer and the drone,” he said.

“That was a really great blow to Kim Jong Un. So [he] thought, what would happen if the same thing happens to him. So there must be a number two.”

The trouble is, all of Kim Jong Un’s children are still very young.

He thinks in the event of Kim Jong’s untimely death, his sister would take the mantle — but only briefly.

“If something happens to Kim Jong Un, I think that Kim Yo Jong would take office,” he said.

“But temporarily — I don’t think that the Kim Yo Jung dynasty would last long.”

Why a woman would be toppled by Pyongyang’s ruling male class

Gang Min Jin is a North Korean defector who now lives in Seoul.

In North Korea she worked for the government in gold trading but now spends her time as an analyst focussed on discovering what is really happening in the country she left behind.

Her contacts communicate with her on contraband Chinese mobile phones which have been smuggled into North Korea.

She also believes any elevation of Kim Yo Jong would be temporary as the upper echelons of power in North Korea would not accept a woman as their ruler.

“You can see that most of party high rankers are male. Considering the power structure of North Korea, even though she is family, Kim Yo Jong cannot be a successor within that system,” Ms Gang said.

Bong Young-shik agrees and compares it to the situation in China during the height of the cultural revolution in the 1960s and 70s.

“It’s very similar to the end of Mao Zedong and his last wife and the Gang of Four,” he said.

The Gang of Four faction was formed by Jiang Qing, also known as Madame Mao, to maintain an iron grip over China’s political institutions.

A month after Chairman Mao’s death, she was arrested by his successor and spent much of her last years in prison.

“The power of the Gang of Four was very impressive, but it has an inherent limitation. Their power was tied to the power of Mao Zedong as a supreme leader,” Mr Bong said.

Similarly, Kim Yo Jong’s power is likely tied to her brother remaining in charge.

“If … grave things happened to her brother and the power vacuum [was] created, then Kim Yo Jong may be a short-term stop-gap. But nothing more than that.”