WASHINGTON - In less than two years Donald Trump has gone from real estate tycoon and reality TV celebrity to the brink of negotiating with the leader of a nuclear-armed foe with whom he has exchanged threats and insults - North Korea's ruthless but also coldly pragmatic dictator Kim Jong Un.

Mr Trump fancies himself as deal maker extraordinaire and has appropriated the role of chief negotiator. The question is, can he rely on his instincts - which after all brought him the Presidency - to pull off a deal to essentially neutralise Mr Kim's ability to strike the United States with a nuclear warhead?

To say that millions of lives depend on the outcome would be a cliché, but in this case it is not an exaggeration, given that the two countries have been edging closer to the brink for the better part of a year.

Mr Trump's out-of-the-box style has never been so apparent; his decision to meet Mr Kim was apparently spontaneous, stunning diplomatic and policy circles in America, Japan, China and even South Korea, which is now in the unfamiliar role of a mediator.

Summits - the more so with adversaries - normally take months to prepare. Negotiators argue about venues, seating, transport, security, and every comma and semi-colon in the draft texts of agreements and declarations.

Only when the broad outcomes are essentially settled, but for key issues that need a face to face nod, do heads of state or government meet for a usually tightly scripted event.

President Trump has flipped that around, presenting his diplomats with a fait accompli.

That is not atypical, and should not have come as a surprise. America's goal has not wavered from complete and verifiable denuclearisation of North Korea, but Mr Trump has said before that he would be ready to talk with Mr Kim if the latter pledged to denuclearise.

He is already known to prefer speaking frequently and directly with other leaders - including China's President Xi Jinping - by phone. In this case, why bother with the tension of years of painstaking negotiations by underlings, when he can meet face to face with Kim Jong Un and, guided by a New York tycoon's instinct, settle key issues on the spot?

Mr Trump has been consistently underestimated. He knows how to mix enticement with coercion. He is also clearly an authoritarian at heart, speaking a language other authoritarians or quasi-authoritarians like China's Xi Jinping, Russia's Vladimir Putin, the Philippines' Rodrigo Duterte, and no doubt Kim Jong Un - are not uncomfortable with.

It is clear that Mr Trump also has a yearning to go down in history as a great President. Always a showman, meeting with Mr Kim will give him the sort of grand stage he thrives on.

Of course meeting Mr Kim is a huge gamble. It hands the North Korean leader a propaganda coup. Negotiations on deliverables may bog down on any number of contentious issues.

The shadow of great power rivalry hovers; China would be happy to see North Korea denuclearise at least to some degree, perhaps in exchange for a reduction of US troops on the Korea peninsula. North Korea will be happy to open a channel of communication with the US, sidelining China - and happier still if Mr Trump goes against decades of orthodoxy and leaves the peninsula to the devices of Koreans.

But complete and verifiable denuclearisation is counter intuitive; why would Mr Kim give everything up after having come such a long way, and moreover surrounded by big powers Japan, China and the United States?

Kim Jong Un wants to be bought off, according to Mr Daniel Russel, the State Department's former top diplomat for East Asia and the Pacific who is now a senior fellow at the Asia Society in New York. "What we may be starting is the haggling phase," he told Pod Save The World this week. "It's a familiar overall pattern."

Mr Kim may hope that the "playbook of provocation, then peace offensive, then negotiation and concession" will work, Dr Sue Mi Terry, Senior Fellow at the Centre for Strategic and International Studies (CSIS) in Washington told The Atlantic.

Few if any diplomats have as extensive experience in negotiating with North Koreans than former US Ambassador Mr Christopher Hill, author and currently chief advisor to the Chancellor in Global Engagement at the University of Denver. His advice: expectations must be calibrated.

Any US President could have said he would meet the North Korean leader and the latter would be delighted, Mr Hill told The Straits Times. "The real question is, is this meeting going to be a one off, or will it usher in an era in which North Korea actually reduces their arsenal and rejoins the international community?"

"There are some hints that North Korea is interested in putting their nuclear weapons on the table, that's certainly something new for Kim Jong Un. But for those of us who have spent a lot of time negotiating with the North Koreans it's not new."

But he acknowledged: "This is really quite an extraordinary development, to be sure. I think it's worth a try. I don't see anything else that was such a compellingly good idea."

From where Mr Trump sits, Kim Jong Un is in a spot - under onerous sanctions, a hostile international community, and a far more powerful United States under a leader who enjoys a fight and is apparently quite ready to use overwhelming force.

But just as Mr Kim would be making a mistake to underestimate Mr Trump, the reverse is also true. "What is happening now is Kim Jong Un's play," Mr Russel cautioned on Pod Save the World. "He's driving this."

President Trump often plays fast and loose with facts and details. But he is equally known for the blunt candour that endears him to his middle American support base.

There was such a moment at Saturday night's rally in Pennsylvania when he told the crowd that when he meets Mr Kim, "I may leave fast, or we may sit down and make the greatest deal for the world."