Boris Johnson faces knotty diplomatic challenge in Brexit deal talks

Boris Johnson is flying to Belfast to try to sort out the consequences of a Brexit deal he signed.

Those consequences - known as the protocol - include checks on stuff crossing from England, Scotland and Wales to Northern Ireland and, still, no fully devolved government at Stormont.

So what's he trying to achieve?

Think of it as four-dimensional diplomacy. At least.

Here are the moving parts:

The Democratic Unionist Party, who hate the protocol because they see it as detaching Northern Ireland from the rest of the UK. They won't go back into power sharing government at Stormont unless it changes.

The European Union, who say, 'Look you signed this international agreement Boris Johnson, don't try to unpick it now'.

The White House and political opinion in Washington, plenty of whom don't like the idea of the UK shredding the Protocol.

And views within the government at Westminster vary significantly, stretching from hawks tempted by a scrap with Brussels, to others who fret that might be counterproductive.

When some within government are describing others within government to me as "knuckleheads", you can be confident there's lively debate internally about how to manage this.

Expect the prime minister's language today to be emollient. We've had a flavour of that already in the long article he's written for the Belfast Telegraph.

This isn't about scrapping the protocol, the prime minister says, it's all about a desire to "make it work" as he sees it.

Those who study the fine print of this stuff point not just to Article 16 that allows either side to suspend the protocol, but also Article 8 which talks about changes to it or it's eventual replacement.

Expect this to get a mention when some respond to the UK's plan to legislate by claiming it is a breach of international law. Not so, will be the counter argument, it is operating within it.

So after the prime minister's dash to Belfast, expect the Foreign Secretary Liz Truss to set out on Tuesday the plan for a new law.

I'm told it will be a "first principles declaration of intent".

In other words this isn't a hurtling towards the Statute Book, banging out a new law for immediate enactment and implementation.

It is hoped it is a twin track strategy: keep talking to the European Union, but have a backup plan too.

But we know what plenty in Brussels think: that the UK is trying to renege on an international agreement if signed, that it is acting in bad faith and can't be trusted.

Privately, there's an irritation among some ministers that the EU is still seeking to punish the UK for Brexit.

How come Brussels has managed to be so admirably open minded and flexible in welcoming so many from outside the EU - fleeing Ukraine - one senior figure said to me, and yet they're so dogmatic about a relatively trivial border on the island of Ireland?

But the EU insists the UK freely chose to sign this deal and it should live with it.

There's a hope from some in government at Westminster that the next few days - the prime minister's visit today and a speech from the foreign secretary tomorrow - might be enough to tempt the DUP to allow the nomination of a Speaker at Stormont.

In other words, politicians now being paid actually being seen to do some work.

But they wouldn't be scrutinising a fully functioning Executive, which remains in caretaker form.

It would only be a first step.

But it would be one that demonstrated some momentum.

The route map after that looks like this:

Talks continue with the European Union, with a focus on trying to ensure stuff crossing the Irish Sea that is only for Northern Ireland gets across without delay. It is what some are calling a 'green lane'.

Talks continue in Washington - don't be surprised if there's another ministerial visit there soon - to continue making the case there to an often sceptical ear that the UK is behaving reasonably.

The legislative process begins at Westminster, but not in a colossal hurry.

And then the focus returns to one question: what will the Democratic Unionist Party do?

Some worry they will always find an objection in the protocol to use as an excuse to avoid going into government with a Sinn Fein first minister.

There is a range of instincts within the DUP on this, for now they wait to see what action, rather than words, is forthcoming.

And they argue they won their seats at Stormont on an unflinching mandate about the protocol, and they're now seeing that through.

A change in the law in February gives Northern Ireland's politicians six months to come to a deal to restore full devolution.

That clock has just started ticking. At the end of that six months, the Northern Ireland secretary then has a 12 week window in which to call another election.

The political quandary the DUP will face, at some point, is do they accept whatever changes to the protocol the UK can secure, or not?

How much credit will they get for standing up for their principles on the protocol?

How much criticism will they get for blocking the return of fully devolved government?

Because remember, for all the noise and all the international diplomacy, at the heart of all this is how Northern Ireland is run - or not - day to day.

A Northern Ireland where, to pick just one example, the NHS is under greater pressure than anywhere else in the UK.

Where, as things stand, there is a caretaker Executive able to do very little, and a load of newly-elected politicians, being paid by the taxpayer, to do very little.

The path from here to fully functioning devolved government in Northern Ireland and an arrangement on the protocol that both the UK and the EU is happy with could be rather long, and with more than a few twists.