In the wake of the pageantry surrounding U.S. President Donald Trump’s historic summit with North Korean leader Kim Jong Un, questions over the substance of a vaguely written denuclearization deal lingered as some experts and former officials anticipated how the White House might beef up the bare-bones agreement.

Trump on Wednesday thanked Kim in a series of tweets “for taking the first bold step toward a bright new future for his people” a day earlier, writing that “The World has taken a big step back from potential Nuclear catastrophe!”

The words of praise stood in stark contrast with earlier threats of “fire and fury” by the mercurial U.S. president and came on the heels of a joint statement a day earlier that Trump hailed as a “comprehensive document” that would kick-start “the beginning of an arduous process.”

That agreement secured a vow from Kim that his country would work hand-in-hand with the U.S. “towards the complete denuclearization of the Korean Peninsula,” among other lofty goals, but said much of the details would be handled in follow-up negotiations led by U.S. Secretary of State Mike Pompeo and North Korean officials to be held “at the earliest possible date.”

Mark Fitzpatrick, a veteran arms control expert with the International Institute for Strategic Studies in Washington, called the deal a “nothing burger” in a commentary posted to his think tank’s website, ripping the short, four-point joint statement for saying “nothing about missiles, chemical and biological weapons, human-rights abuses, abductions or other issues of concern.”

“Even ‘denuclearization’ is put in terms of ‘working towards’ this goal,” he wrote.

Jung Pak, a senior fellow at the Brookings Institution in Washington wrote on the think tank’s blog that “the Singapore summit produced little more than frothy statements without substance, with little accountability for Kim Jong Un to cease and dismantle his nuclear weapons program. Even so, she wrote, it was entirely likely that the Trump administration would “tout this as a Nobel-worthy effort.”

According to Pak, who worked as a Korea analyst at the CIA until last year, Trump could have used the summit as an opportunity to reinforce Washington’s commitment to its alliances with South Korea and Japan, “but instead made gratuitous comments complimenting Kim and touting his trustworthiness, as well as raising the possibility for more giveaways” to the North Korean dictator.

Tokyo and Seoul, already nervous after a year that saw Trump and Kim push the Korean Peninsula to the brink of war, have grown accustomed to the U.S. president’s erratic behavior, but remain wary that he could in an instant make alliance-altering decisions without their consultation.

Indeed, Trump appeared to highlight these fears Tuesday with a seemingly out-of-the-blue decision to halt joint military exercises with South Korea. That surprise announcement caught not only Seoul and Tokyo off guard, but also the U.S. military in South Korea.

For Japan, Philip Yun, a North Korea expert and executive director at the Ploughshares Fund in San Francisco, said Trump’s follow-through on a pre-summit promise to raise the issue of Japanese nationals abducted by North Korean agents in the 1970s and 1980s “was easy for the president.” But Yun noted that since it was not mentioned in the statement, it was not clear how much energy had been devoted to any discussion.

As for shorter-range missiles capable of striking Japan — a top concern of Tokyo’s that appeared conspicuously absent from the summit discussions — Yun said that the issue “may have been too much to discuss for now,” but added that it would need to be addressed in any subsequent talks.

Kim announced in May that the North would halt launches of intercontinental ballistic missiles (ICBMs), a decision that left open the possibility of tests of short- and intermediate-range weapons, including the hundreds of Rodong missiles it is believed to possess.

“The U.S. cannot pocket a moratorium on ICBMs without addressing the short-range missile issue,” Yun said. “But realistically, a solution to the short-range missile threat — because there are so many — is a difficult issue and will take time to resolve.”

Patrick McEachern, a fellow at the Wilson Center think tank in Washington, said it was important to distinguish between expectations for the Singapore summit and the end result of what he said was likely to be a “long and difficult diplomatic process ahead.”

“The summit restarted long-defunct diplomacy and dramatically showed the two leaders are vested in its success,” said McEachern, who is also a former analyst on North Korea with the U.S. State Department.

“Most summits are a capstone to lower level meetings, allowing the leaders to showcase specific accomplishments,” he said. “This meeting was different, since it was at the beginning. We should not expect capstone summit outcomes from Singapore.”

Typically, summits such as the Kim-Trump meeting, as well as detailed goals, are hashed out by lower-level officials and experts. Trump turned this approach on its head by starting from the top.

“The Trump-Kim summit was an opportunity to set broad goals and unmistakably direct both leaders’ senior officials to pursue them,” McEachern said, adding that any attempt by the two leaders to negotiate specifics on such a complex issue would been “a train wreck.”

McEachern framed the summit as “the grand opening ceremonies for this important diplomacy,” saying that “senior officials with the leaders’ confidence and technical and regional experts in tow can now get to work.”

But while some commentators praised the return to somewhat solid diplomatic footing and away from the threat of nuclear war, others cautioned that Trump’s meeting with Kim and the growing detente between the two nations was a win-win situation for the North Korean leader.

They said Kim had gained what he had long craved: recognition of the North on the global stage as a de facto nuclear power and normal state, while at the same time leaving him with an escape route if things went sour on the diplomatic front.

Sung-Yoon Lee, a Korea expert at The Fletcher School at Tufts University in Massachusetts, said viewing the decisions at the summit as a welcome respite from talk of war “ignores the pitfalls of illusory diplomatic progress that grants Kim time and money with which to grow his nuclear lethality.”

Indeed, concerns over apparent concessions by Trump at the summit emerged Wednesday as North Korea said that the U.S. president had explicitly acceded to two of Kim’s most sought after goals during the talks.

Despite this, the Ploughshares Fund’s Yun, who was part of the U.S. delegation that traveled to the North with then-Secretary of State Madeline Albright for a landmark visit to Pyongyang in October 2000, said that while he agreed that the results of the summit were “unclear and lacking in detail,” Tuesday’s meeting was part of an ongoing process.

“I am willing to hold judgment for now; but we must have a clear sense of what North Korea means by denuclearization — both to timing and scope. This in the end is how we judge this process,” Yun said.

“That being said, we are clearly on a very different footing now than six months ago — many thought the U.S. was on the path to a possible war with North Korea; for now this has been averted, understanding it could change quickly,” he said. “Let’s not forget this.”