(CNN) South Korean President Moon Jae-In landed in Washington Monday to do what he can to shore up plans for a US-North Korea summit that seem to be on shaky ground.

Moon will meet with Donald Trump Tuesday, ahead of the US President's planned summit with North Korean leader Kim Jong Un in Singapore next month.

Analysts say Moon will be looking to hold Trump to the diplomatic approach the South Korean leader has championed and invested considerable political capital in, amid heightening skepticism over the talks in Washington. Last week, Trump appeared to suddenly catch up to widespread skepticism over how willing Kim will be to give up his nuclear arsenal.

The White House last week was forced to downplay comments by Trump's national security adviser John Bolton that North Korea could follow the "Libya model" in denuclearizing, after they received an angry response from Pyongyang

Trump said North Korea would never be overthrown by western powers, as Libyan leader Moammar Gadhafi was in 2011, if it agreed to give up its nuclear weapons. But the remarks still rankled in Pyongyang, and spoke to an apparent lack of understanding by Trump and those around him of North Korea's intentions going into the Singapore summit.

The first big test of whether things are truly off track will come this week, when North Korea is due to destroy the Punggye-ri nuclear test site , in full view of international observers and journalists. Calling off that event, praised by Trump as a show of good faith, would be a major blow to ongoing negotiations.

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Danger of a failed summit

Ahead of the Singapore talks, many experts on North Korea have pointed to a disparity in what both sides seem to expect from the summit.

While North Korea has been willing to discuss denuclearization, Pyongyang has not yet said it will agree to do so in Singapore, and, most importantly, it has always spoken of the denuclearization of the entire Korean Peninsula . This would mean the removal of the US "nuclear umbrella" over South Korea, not just the unilateral disarmament of North Korea.

Pyongyang's angry reaction to Bolton's Libya comments had led to suggestions from some in Washington that it had backtracked or altered its position, but this is completely inaccurate, Jeffrey Lewis, an arms control expert at the Middlebury Institute of International Studies, wrote Sunday

"North Korea's position never changed. Our interpretation of the exact same words changed," he said. "This is a fiasco of the White House's own making and we should not let them shift the blame to Pyongyang."

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Denuclearization was always bound to be the biggest sticking point in any talks with North Korea. The White House had indicated it would be willing to assist North Korea economically if it gave up its nuclear weapons, but was clear any other steps would be a non-starter without denuclearization happening first.

While denuclearization as a first step has long been US policy, on Saturday , James Clapper, a former director of national intelligence under Barack Obama, said this was a mistake.

"We should meet their demand to sign a peace treaty, and establish a physical presence in Pyongyang, an office staffed by Americans who can interact with North Korean citizens," he said.

"It would not be a reward for bad behavior, but an opportunity for access, which would enhance our understanding and enable the flow of information from the rest of the world."

Many experts on North Korea have expressed alarm over the speed of negotiations and Trump's reported unwillingness to be briefed on some key issues. Robert Kelly, a professor of political science at South Korea's Pusan National University, told CNN there was a "real competence gap on the American side."

"The Trump administration is going into this very, very quickly," he added, saying the most sensible solution would be to slow things down, postpone the meeting for six to eight months, and allow negotiators to "hammer out a framework to narrow the differences between the two sides."

A failed or acrimonious meeting in Singapore could "make things worse," Kelly said. "The hawks on both sides can say 'I told you so.'"

One of those hawks, US Senator Lindsey Graham, seemed to be preparing to do just that Sunday, telling Fox News that if Kim didn't show up to the summit "that puts us back on the path to conflict."

"President Trump told me three days ago that he wants to end this in a win-win way," Graham said. "He thinks that's possible."

"If they don't show up, that's the end of diplomacy. If they do show up and try to play Trump ... that means military conflict is the only thing left. And if we have a conflict with North Korea, they will lose it, not us," he added.

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Moon's moment

Doubts over the Singapore summit put the onus on Moon, who has been encouraging engagement with North Korea since his election last year, to get things back on track. Trump and Moon discussed North Korea in a call Saturday, ahead of their meeting this Tuesday.

Kelly said the Moon administration will be "very concerned about the possibility of backsliding into 'fire and fury'."

"My guess is Moon is going to try and keep Trump tied to the diplomatic track," he added, pointing to South Korea's frequent praising of Trump and even suggestions he could receive a Nobel Peace Prize for a successful deal with Kim. "All this stuff is designed to stop Trump starting a war."

After an historic summit between Moon and Kim last month , and Moon's intense negotiating in getting Trump to the table, South Korea's role has diminished significantly, leading to some concern Seoul's achievements could be undone by the other parties.

"It was clear from the start that North Korea would treat the inter-Korean summit differently from its meeting with the US," said Anwita Basu, an analyst with the Economist Intelligence Unit (EIU).

"The parties set to lose the most if the US-North Korea talks collapse are South Korea and China. Both are eager to support the North Korean economy and defuse the tensions around the regime's nuclear program through diplomacy and negotiation. With hawkish players leading the US administration and extreme distrust in North Korea, such hopes might be quickly quashed."

Basu predicted Moon could look to China for support on ensuring the talks go ahead, "otherwise all this show of diplomacy will boil down to nothing."

Speaking last week, Trump suggested Chinese President Xi Jinping could be "influencing Kim Jong Un," and encouraging the North Korean leader to take a more strident tone.

Many analysts dismissed this however , pointing out North Korea's position had not shifted significantly, and an improved relationship with Beijing did not mean China could pull the strings.

"There's always a temptation to see North Korea as a pawn in China's game but the North Koreans have their own play here and Kim Jong Un's not just going to do Xi Jinping's (bidding)," said John Delury, associate professor at Seoul's Yonsei University.