The nightmare scenario heading into the second summit between President Donald Trump and North Korean leader Kim Jong Un isn’t so much “fire and fury” and millions dead. Rather, some experts fear the meeting could result in an ill-considered deal that allows North Korea to get everything it wants while giving up very little, even as the mercurial leaders trumpet a blockbuster nuclear success.

There’s little argument that just sitting down together again in the same room this week in Hanoi is a positive sign for two men who seemed to be flirting with a second Korean War in 2017, and there is, as the White House trumpeted ahead of the summit, “a tremendous opportunity” here to address a monumental problem that’s flummoxed generations of policymakers.

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But with the stakes so high, a growing chorus of experts highlight a particular risk: that Trump, burned by criticism that the results of his June meeting with Kim in Singapore were vague at best and an outright failure at worst, will ignore his more cautious aides and try to strike a deal that’s cobbled together on the fly with little preparatory work.

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Why is this potentially dangerous? Because when it comes to North Korean nuclear diplomacy, all deals are not created equal.

A look at some of the anxieties that are swirling ahead of the Hanoi summit:

Worry no. 1: A piecemeal deal

South Korean papers have been filled with unidentified government sources suggesting that Trump and Kim might strike a deal that stops far short of the road map for the full denuclearization of the North that the United States has long insisted on.

Instead, Kim could agree to give up only part of his arsenal — his intercontinental missiles aimed at America, for instance, or his main nuclear reactor — in return for an easing of harsh sanctions. There’s also fear that Trump will eventually orchestrate some sort of drawdown of U.S. troops from South Korea or an extended halt to U.S.-South Korean military drills.

Chairman Kim realizes, perhaps better than anyone else, that without nuclear weapons, his country could fast become one of the great economic powers anywhere in the World. Because of its location and people (and him), it has more potential for rapid growth than any other nation! — Donald J. Trump (@realDonaldTrump) February 24, 2019

For Trump, such a deal could generate a much-needed rush of “breakthrough” headlines to help distract from swirling investigations in Washington while helping assure his supporters that he’s protecting the American mainland.

Kim, for his part, would be taking a huge step toward cementing the North as a nuclear weapons state and, as a bonus, driving a wedge in the U.S.-South Korea alliance that the North maintains is aimed at the overthrow of the Kim family — all without addressing the North’s arsenal of short- and mid-range nuclear armed missiles aimed at Seoul, Tokyo and other parts of Asia.

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WATCH: Trump looks ahead to Kim summit

2:33 ‘The relationship is very strong’: Trump looks ahead to Kim summit ‘The relationship is very strong’: Trump looks ahead to Kim summit

Those in favor of this kind of piecemeal deal say it’s simply a matter of accepting reality: North Korea won’t give up nukes it sees as crucial to deterring what it calls U.S. hostility, so the wise move is to work to first limit or freeze the program’s most worrisome aspects and then work toward total denuclearization.

Skeptics say this would give the North too much in return for too little. They want instead something that first forces Pyongyang to list the particulars of its nuclear program, then allows outsiders to verify the list and see the program demolished.

READ MORE: Why peace would be a win for North Korea

“Ad hoc deals or piecemeal negotiations absent an agreed-on road map would allow Pyongyang to dictate the terms, pace and duration of the diplomatic process without making a dent in North Korea’s nuclear arsenal,” Duyeon Kim, a Koreas expert at the Center for a New American Security, recently wrote.

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“There is a serious risk of Trump ad-libbing his way into a bad deal, as he did in Singapore in June 2018, by relinquishing vital bargaining chips that disadvantage U.S. interests and Asian allies’ security,” she added.

Worry No. 2: Kim and Trump are too aligned

There’s a joke being shared by some North Korea experts: Did you hear that Kim Jong Un and Donald Trump both want the same thing from their Hanoi summit? The United States out of South Korea.

Funny or not, the dark humor gets at serious doubts churned up by Trump’s repeated public expressions of a deep wariness about the U.S.-South Korea alliance that many in Seoul and Washington see as a lynchpin of Northeast Asian security.

WATCH: Trump discusses upcoming North Korea summit, says progress being made

2:05 Trump discusses upcoming North Korea summit, says progress being made Trump discusses upcoming North Korea summit, says progress being made

The best example may be Trump’s stunning announcement in Singapore of the suspension of annual military drills by Seoul and Washington that North Korea rails against as “invasion preparation.”

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Trump called the drills “very provocative,” mirroring North Korean language.

Although his lieutenants say the removal of American troops isn’t on the agenda in Hanoi, Trump has said that he wants to eventually bring home the 28,500 troops stationed in the South. Just this month Trump said: “South Korea — we defend them and lose a tremendous amount of money. Billions of dollars a year defending them.”

Worry No. 3: North Korea hasn’t changed

There’s also alarm that Trump and South Korea’s dovish president are misreading North Korea.

“Kim is not going to unilaterally surrender his nuclear weapons,” Vipin Narang, a North Korea nuclear expert at MIT, said in an interview. “It is now pretty clear that Trump doesn’t care that Kim isn’t going to unilaterally disarm, so long as he doesn’t embarrass Trump by visibly flight testing missiles or openly testing nuclear weapons.”

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Despite the positive spin on North Korean intentions by the liberal government in Seoul, critics say, Pyongyang, as it has since the Korean War, still claims to be the sole legitimate Korean government, and is therefore working to split South Korea from its U.S. protector and enshrine its nuclear program, even if partially, as a way to eventually coerce Seoul into doing its bidding.

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North Korea has famously called its nuclear arsenal a “treasured sword.” And a senior North Korean official said last year that dialogue won’t continue “if the U.S. is trying to drive us into a corner to force our unilateral nuclear abandonment.”

WATCH: U.S. envoy hints at compromise in North Korea nuclear talks

1:45 U.S. envoy hints at compromise in North Korea nuclear talks U.S. envoy hints at compromise in North Korea nuclear talks

Asked at a recent press briefing if the North was negotiating in good faith, a senior U.S. official who refused to give his name under White House rules said: “I don’t know if North Korea has made the choice yet to denuclearize. But the reason why we’re engaged in this is because we believe there’s a possibility that North Korea can make the choice to fully denuclearize.”

Trump tweeted Sunday that he and Kim “both expect a continuation of the progress made at first Summit in Singapore. Denuclearization?”

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Still, there are big doubts about the North’s intentions.

When the two leaders meet in Hanoi, Kim “will further ensnare Trump on his march toward full nuclearization, compelling Trump to make more concessions like a peace agreement and drawdown of military support for South Korea,” said Sung-Yoon Lee, a Koreas expert at Tufts University. ”‘Peace’ sounds very pleasant, even hypnotically alluring, but a peace agreement between the U.S. and North Korea and allowing Kim Jong Un to buy more time only increases the chance of war.”