In a jaw dropping presidency has there ever been a more jaw dropping moment than the moment last June when Donald Trump walked in from the right and Kim Jong-un came in from the left, and shook hands in Singapore?

The two gunslingers, little rocket man (as Trump had called Kim), and the mentally deranged dotard (as Kim had called Trump) about to parlay. It was extraordinary, not just because of the improbability, but also because there has probably never in history been a summit so ill-prepared.

Right up until the last minute, there were a lot of administration officials urging delay. There was no agenda for the talks, no draft communique, no agreed modalities. What were they aiming to achieve?

Why are you giving the reviled leader of a brutal dictatorship that has flouted all UN rules on nuclear proliferation a platform like this on the world stage? Conventional politics and normal diplomatic procedure was screaming "don't go near this".

But Donald Trump isn't that conventional leader. He wanted to roll the dice and see what happened.

I'm told that on the flight over on Air Force One, Donald Trump was fixated on just one thing.

No, not what the complete denuclearisation of the Korean peninsula actually meant in practice; nor was it about what package of economic assistance he would offer as an incentive.

Certainly little time was spent discussing confidence building measures. No, he was obsessing about the moment when he and Chairman Kim would meet - where would the cameras be positioned; what was the backdrop; how was their entrance going to be orchestrated.

If this first meeting was going to be theatre, it had better be good theatre.

The other thing that caused officials deep unease was that the US president and North Korean leader would start by meeting alone.

What might a freewheeling Donald Trump agree to - no one had any idea. At a news conference we found out - but astonishingly it was breaking news for the South Korean leadership and the Pentagon too - they'd had no warning - but the president had agreed the Americans would put a halt to all military exercises on the peninsula.

He also talked about them as a provocation - words that could have fallen from the lips of the Chinese or North Korean leadership.

Yes, the North Koreans would return the remains of US servicemen killed in the Korean War, yes there'd be no more ballistic missile tests - but that was about it from the North Korean side.

Virtually everyone scored the summit - and that announcement on military exercises in particular - as a huge victory for Kim.

Needless to say, Donald Trump hadn't marked it like that, and his mood darkened as he travelled back to the US, and saw the coverage. He would declare on Twitter "Just landed - a long trip, but everybody can now feel much safer than the day I took office. There is no longer a Nuclear Threat from North Korea."

Except nothing had changed in North Korea's nuclear arsenal, and no promises had been made - so last weekend, the US Secretary of State, Mike Pompeo was pressed on that point. He sought to argue that that is not what the president had said, and sought to reinterpret what it was the president actually meant.

And though the goal is still the complete denuclearisation of the Korean peninsula, US officials who gave a briefing call to journalists last week acknowledged there isn't even agreement about what denuclearisation actually means, let alone how to get there.

In other words, eight months on from Singapore, they still haven't defined terms. These officials also refused to be drawn on any deliverables that might come from Hanoi. This was expectation lowering.

That said a lot of serious thought and effort has gone into making progress, and what might be realistic to hope for from Hanoi.

Could there be some kind of deal in which North Korea promises to halt all work at its nuclear facility at Yongbyon, and allow inspections in return for some kind of sanctions relief?

Would the US be prepared to declare that the Korean War is over - a longstanding demand of the North Koreans? Also how do you verify something when you don't know precisely what the Koreans have? Sure there are estimates of how big Kim's nuclear arsenal is, but does anyone have hard facts?

On the streets here in Hanoi, there is a buzz about their city, with its complex history, being the centre for this latest summit. Even an economic model of what North Korea might become. But will big things be decided over the coming days that will reshape the future geopolitics of the peninsula, or will it be another occasion that is more theatre than substance?

Last time round it was a marvel - and enough - to see the two smiling and shaking hands. But maybe the more realistic explanation is that another small step will be taken here. Maybe there will need to be many more summits between these two unlikely peacemakers.

Donald Trump is said to be in no rush. Just as well. This will take as much careful navigating as getting through Hanoi's rush hour traffic.