But with only days to go before the meeting, analysts say there are issues remaining that could still derail the on-again, off-again summit or lead to the leaders walking away during their talks on June 12 in Singapore.

The most significant challenge appears to be closing gaps on the timeline and process of North Korea’s denuclearization before the summit.

“The biggest variable would be whether North Korea agrees to ship parts of its nuclear warheads, nuclear material and intercontinental ballistic missiles out of the country, and to allow unconditional, random inspections of the country’s nuclear facilities,” said Shin Beom-chul, a senior researcher at the Asan Institute for Policy Studies.

Five rounds of working-level talks between the US and North Korean delegations have been held at the border village of Panmunjeom since May 27. It was not confirmed whether the officials met again Tuesday.

The two sides appear to agree that Pyongyang denuclearizes in return for a security guarantee from the US in a short period of time, possibly by 2020. But they seem to be at odds over what should be front-loaded in the denuclearization process at the working-level talks.

Analysts say the US wants North Korea to agree to transfer some of its nuclear weapons and missiles out of the country within months. North Korea is thought to want the US to lift sanctions against it and begin taking steps to open diplomatic relations with the communist state.

Another issue that could complicate the high-stakes diplomatic game could be China, Shin said.

“If China wants to play a role and join South Korea, North Korea and the US in declaring an end to the Korean War, it could arrange a meeting with North Korea before North Korea-US summit to pressure the isolated country to include China in the process,” he said. “In return, China could promise sanctions relief.”

Declaring an end to the Korean War is thought to be a precursor to ending hostilities and establishing a peace regime on the Korean Peninsula -- the first step to guaranteeing the North Korean regime’s survival.

China has signaled its growing unease at being sidelined in discussions over a declaration of the end to the Korean War through its state-run media.

“As China is one of the signatories of the armistice, its participation in formulating and signing a declaration to end the war is essential to ensure its legal and historical status,” China’s state-run English-language news outlet Global Times wrote in an editorial published Monday.

Seoul’s presidential office has said that China could be left out of the process of declaring an end to the Korean War, but added its role is essential in signing a peace treaty with the North. China appears to be struggling to retain influence over issues concerning the Korean Peninsula -- key leverage over the US.

North Korea’s human rights situation could be another challenge in US-North Korea negotiations. With Trump expected to focus on getting a nuclear deal, concerns are lingering that North Korea’s human rights will be overlooked at the summit.

White House officials are reported to have said that the plight of the North Korean people, who live under one of the world’s most repressive governments, is not a priority at the summit. But Trump said Friday he “probably” would bring up human rights when he meets with the North Korean leader and maybe “in great detail.”

“As North Korea will react angrily if the US brings up the issue of North Korea’s human rights, Trump will likely not raise the issue during the summit. Even if he does, I think that Trump would just lightly touch on it,” said Kim Hyun-wook, a professor at National Korea Diplomatic Academy. “I don’t think it will be a major variable this time.”

But to give the level of protection North Korea wants -- such as sanctions relief, normalization of relations with the US and the signing of a peace treaty -- any deal coming out of the summit needs to be approved by the US Congress.

Mindful of North Korea’s security concerns, US Secretary of State Mike Pompeo testified that he hopes any deal reached during the summit is sent to Congress to be approved as a treaty -- a formal and written agreement between sovereign states. Treaties must be approved by a two-thirds vote in the Senate before the President can ratify it.

However, experts say prospects of the deal brokered at the Singapore summit getting approval from US Senate appear to be dim, unless the deal touches on North Korea’s human rights -- which the reclusive regime considers a threat to its regime and authority.

“The biggest variable to watch out for is ... whether the US can guarantee the level of protection North Korea desires. Unless North Korea makes concessions significant enough to persuade the US Congress, it will be tricky for the US to promise a security guarantee North Korean wants,” said Park Won-gon, a professor at Handong Global University.

Senate Democrats on Monday released a letter to the Trump administration outlining the parameters of what they believe constitutes a satisfactory agreement. Their demands include dismantling and removing the North’s nuclear, chemical and biological programs, a suspension of ballistic tests, and robust inspections.