Nic Robertson is CNN's international diplomatic editor. The opinions in this article belong to the author.

As June 12 nears, the Trump-Kim summit planned for that day teeters in the balance.

US Secretary of State Mike Pompeo struggles against the clock to keep the talks on track as Russia calls for a slowdown.

While Pompeo was meeting Kim Jong Un's top negotiator in New York, Pompeo's Russian counterpart, Sergei Lavrov, was in Pyongyang, visiting leader Kim Jong Un.

Immediately afterward, Lavrov disingenuously declared, "We don't consider it our right to interfere" -- then promptly did just that, saying, "It is very important to approach these contacts extremely delicately, not to try to make sudden moves, to artificially speed the process." It was a clear shot at President Trump's high-speed diplomacy.

Back in March, Trump could barely contain himself. In the space of 45 minutes, he took the decision he may yet rue for the remainder of his presidency.

South Korea's national security adviser had hotfooted from the DMZ to DC with an invitation for Trump from Kim for a summit.

Minutes after receiving the letter, in what has become the biggest foreign policy play of his presidency, Trump stopped by the White House press corps to tease his decision to accept.

Yet the weeks since have exposed Trump's thinking as soft-boiled. Kim offered nothing new on denuclearization. The lack of such concessions was the reason no previous US president rewarded North Korea's long-held desire for a one-on-one summit.

Mystery about Trump's decision

What caused Trump to so quickly agree to take the meeting is a mystery. Had he concluded that his hectoring of "little rocket man," as he liked to call Kim, aided by his threats of "fire and fury," had painted himself into a diplomatic corner?

Did he feel he was cleverly executing a diplomatic version of his art of the business deal -- berate, belittle and bemuse his opponent before closing in on his own terms to seal the deal? Or was his calculation that Kim was calling his bluff and he needed to match?

Did he think the United States' superior forces provide sufficient leverage to get Kim to capitulate -- that Trump had a position of strength? Did he calculate Kim was desperate enough to take the economic carrots he could dangle?

We may never know how Trump rationalized it to himself, although from everything he has exposed about himself since being in office we can guess his oversized ego played a role.

What is for sure is that Kim's economy is hurting, and Trump's nuclear weapons are bigger.

But Kim is not the type of adversary Trump is used to. He is not a businessman looking to build an apartment block. He is descended from a line of dictators and has built a nuclear bomb to protect his interests.

He wants power over North Korea in perpetuity -- security, survival of his family's dynasty and the money-making privileges that go with it.

The Singapore summit has been on, then off, and now seems maybe to be back on. Bizarrely, the issue fouling up the plans is nothing new for American presidents, or their diplomats. It is North Korea's nukes.

For 15 years North Korea's leaders, Kim's father and now Kim, have been saying they are ready to "denuclearize the Korean peninsula."

Rumors have circulated that South Korean President Moon Jae-in oversold Kim's offer of a summit with Trump, but Moon is well versed in the nuance of North Korea's language and logic and would have known its limitations.

Since the summit was announced, Moon has benefited politically. His popularity has risen -- not that he needs to cash in on it right now, since he has four more years in office. His gains spring from widely held fears in South Korea that Trump is more unpredictable than Kim, and the US President's rhetoric last year was so dangerously close to triggering war and a massive loss of Korean life that de-escalation of any type was paramount.

But as the days go by and developments continue, Trump's hasty decision in March is beginning to look more and more like his failure to understand the details of what he was getting into.

He rolled the dice in a high stakes gamble where he is the only rookie at the table.

And as the world witnessed in his letter to Kim pulling the plug on the summit this past week, he is willing to double down to keep the talks in play. The letter was novel in the extreme, mixing praise -- "I felt a wonderful dialogue was building up between you and me" -- and crude threats: "You talk about your nuclear capabilities, but ours are so massive and powerful I pray to God I never have to use them."

Yet in the final paragraph, Trump sounds almost desperate: "If you change your mind having to do with this most important summit, please do not hesitate to call me or write."

Kim did, Trump liked it, and here we are, days to go and gaps still to be narrowed.

Back in March, Trump was ready to get into talks with Kim almost immediately and was held back only by staff, cautioning they needed time to better prepare.

Since then, Trump's administration has been trying to square a circle.

Kim has an extra card

Take North Korea's decade-and-a-half-old declaration of willingness to "denuclearize the Korean peninsula" and make it fit a US desire for North Korea's complete, verifiable and irreversible denuclearization.

On this, Kim is the expert. His family has played this hand again and again with US diplomats. Only now, Kim holds at least one extra card his father never had -- a nuclear bomb, one that he claims he can put in a rocket and hit mainland USA.

Kim has achieved this position of strength not by chance but by design. While both Trump and Moon were tied up winning elections at home in 2016 and 2017, Kim used the time racing for the bomb.

He gambled that neither Moon nor Trump could stop him while he secured the leverage he'd need when he got to the negotiating table.

In this scenario, it was Kim who shaped the conditions to get Trump to face-to-face talks, albeit under the gun of increasingly tough economic sanctions.

In Trump's book, "Trump: The Art of the Deal," the winner is the person who can convince the other he will walk away unless he gets what he wants. Trump's letter to Kim last weekend seems to be a play against Trump's own logic, and so far, Kim seems to be nimbly exploiting him.

Trump's choices seem limited -- walking away from talks now would expose him to justifiable claims he is out of his diplomatic depth.

If his logic is driven by his ego, he'll push ahead, get in the room with Kim where he believes, mano a mano, he will make Kim square the denuclearization circle, delivering, against worsening odds, a first for a US president.

Russia's meddling at this late stage threatens Trump's simple road to talks, yet it might also prove a handy off-ramp. Trump has already explored the blame game -- a few weeks ago, shortly after Chinese leader Xi Jinping held a second surprise summit with Kim in China, Trump accused Xi of upsetting things ahead of the summit.

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It was a wobble, but as face-saving gambits go, it's flawed.

Neither China's nor Russia's interventions should come as any surprise. Both have national security interests at stake; both want to shape US-North Korean relations.

As Trump is discovering, international diplomacy is less egg boiling, more baking a souffle.