(CNN) President Donald Trump's second summit with North Korean leader Kim Jong Un was floundering from the start -- and it ended with a last-ditch effort by the North Koreans to keep the US at the negotiating table and stop Trump from walking away.

As Air Force One made its way toward Hanoi, Vietnam, Secretary of State Mike Pompeo was already on the ground, expecting to meet once more before the summit with North Korea's lead envoy on the nuclear negotiations, Kim Yong Chol. After weeks of negotiations that yielded less progress than US officials had hoped for, Pompeo was eager to gauge North Korea's willingness to strike a deal before Trump sat down with Kim Jong Un.

But Kim Yong Chol, North Korea's vice chairman, wouldn't meet with Pompeo, three US officials and a source familiar with the matter told CNN. The US secretary of state waited several hours hoping Kim would agree to meet, but ultimately turned in for the night, frustrated.

It was not the first time North Korean officials had stood up their US counterparts, but the high-level snub just a day before Trump and Kim were scheduled to sit down was a worrying and ultimately portentous signal that the second summit would not be the triumph Trump had hoped for. Two days later, after a final Hail Mary effort from the North Koreans, it ended without any new agreements and what Trump has come to call "the walk" after North Korea demanded significant sanctions relief in exchange for shutting down one of its major nuclear facilities.

A State Department official told CNN that "There was no expectation, and nothing had been scheduled."

The snub was also indicative of the North Koreans' approach to diplomacy -- a capricious negotiating style that reared its head once again at the end of the summit in the form of a last-ditch attempt from the North Koreans to draw Trump back to the negotiating table.

Unexpected message from Kim

The negotiations were coming to a close at Hanoi's Metropole Hotel when a North Korean official rushed over to the US delegation.

With Trump preparing to leave the hotel, North Korean Vice Minister of Foreign Affairs Choe Son-hui hurriedly brought the US delegation a message from Kim, two senior administration officials and a person briefed on the matter said. The message amounted to a last-ditch attempt by the North Koreans to reach a deal on some sanctions relief in exchange for dismantling the Yongbyon nuclear complex.

US and North Korean officials had been haggling over a shared definition of the sprawling, three-square-mile site and the last-minute overture sought to advance the North Koreans' proposal for dismantling it. But the message did not make clear whether the North Koreans shared the US's expansive definition of the facility and US officials asked for clarity.

Choe rushed back to get an answer. Kim replied that it included everything on the site.

But even when Choe returned with that response, the US delegation was unimpressed and didn't want to resume the negotiations. Within hours, Trump would be wheels up for Washington.

"We had to have more than that," Trump said when asked about Yongbyon before leaving Hanoi. "We had to have more than that because there are other things that you haven't talked about, that you haven't written about, that we found."

The last-gasp effort would still have left the US and North Korea at odds over the extent and pace of sanctions that would be removed in exchange for the nuclear facility's dismantlement. But some US officials believe that the final outreach from the North Koreans is a sign that the Kim is eager to strike a deal -- but whether it's the kind of deal the US would accept remains an open question.

The White House declined to comment for this story.

In his post-summit news conference, Trump argued that he had walked away from a bad deal but insisted that the negotiations had been productive and that this was not the end of the road. And Pompeo, Trump's top deputy in the negotiations, also expressed optimism that the talks will get back on track, arguing that the impasse between the two sides is not insurmountable.

Even as North Korea's Foreign Minister Ri Yong Ho characterized Pyongyang's latest offer as a proposal that "will never be changed," Pompeo told USA Today that the North Koreans are "prepared to continue conversations with us."

"And that's what we intend to do," he said.

US officials questioned Kim's willingness to denuclearize

But ahead of the negotiations, US officials had sought to temper expectations about what could be accomplished during the summit. Working-level talks between US and North Korean officials leading up to it had yielded little progress, and North Korean officials had even threatened several times to cancel the summit.

Top US officials continued to question North Korea's willingness to fully denuclearize and Trump was told that he needed to be ready to walk away if Kim didn't show a readiness to go beyond the position North Korean officials laid out in those lower-level talks.

Still, as Trump headed to Hanoi's posh Metropole Hotel for his first meeting with Kim in eight months, he still trusted in the power of his personal diplomacy with Kim, believing he might be able to charm Kim into an agreement once they met face-to-face. That approach collapsed amid North Korea's demand for relief from the major economic sanctions enacted since 2016 in exchange for dismantling its Yongbyon nuclear complex.

"I just I felt it wasn't good. Mike (Pompeo) and I spent a long time negotiating and talking about it to ourselves. And just -- I felt that that particular, as you know, that facility, while very big, it wasn't enough to do what we were doing," Trump said at his post-summit news conference in Hanoi.

Standing alongside him, Pompeo added: "Even the Yongbyon facility and all of its scope -- which is important, for sure -- still leaves missiles, still leaves warheads and weapons systems. So there's a lot of other elements that we just couldn't get to."

The path forward now remains unclear, with no working-level discussions or a third Trump-Kim summit on the books.

And satellite images released on Tuesday appear to show that North Korea has begun rebuilding a part of a long-range missile test facility, according to analysts from two respected North Korea monitoring websites.

US officials are now working toward organizing the next round of working-level discussions with North Korea within the next month, but North Korea has yet to confirm the timing and location of future talks, an administration official familiar with the negotiations said.

Privately, some of Trump's top advisers on North Korea remain skeptical that Kim will be willing to move close enough to the US position on full, verifiable and irreversible denuclearization. And the latest summit demonstrated the wide gap that remains between the two sides.