Gavin Hewitt

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It is clear that the UK will face a tough divorce from the European Union after European Council President Donald Tusk characterised the forthcoming talks as "difficult, complex" and possibly "confrontational".

From the outset it is clear that the EU side will control the agenda.

That was underlined again on Friday in an early skirmish over procedure. Theresa May wanted divorce talks to run in parallel with negotiations about a future trading relationship. That won't happen.

German Chancellor Angela Merkel had been quick to rule that out and was given swift backing by the French president Francois Hollande. That was reinforced again on Friday with the leak of the European Council's negotiating guidelines.

Why is this so important?

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How do you celebrate in a time of acute anxiety, how do you party in the midst of a family divorce and how do you mark an anniversary when allies predict your demise?

Europe does not know but less than three weeks' time, on 25 March, its leaders will gather in the Piazza del Campidoglio, the square designed by Michelangelo to try to answer those questions.

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Many Europeans eye the months ahead with foreboding. They see anti-establishment parties on the ascendancy. Angela Merkel - for so long Frau Europe - may lose power. And the financial markets are skittish over the possibility of a Marine Le Pen victory in France. Every edge up in her poll ratings sends bond yields rising.

And yet an entirely different scenario may play out. It is quite possible that before the end of the year observers will declare that the Brexit-Trump tide has turned and that European integration has found new champions.

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No modern president has been so analysed. Other leaders don't know him and can't read him. He leaves a trail, but it is strewn with contradictions. He craves popularity but revels in being demonised. He trusts his gut instincts and embraces unpredictability as a virtue.

Diplomats, foreign leaders, business chiefs are all trying to decipher what drives the 45th president.

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There are frequent and regular meetings between British prime ministers and American presidents, but few will have been as significant as the visit to Washington this week by Theresa May.

It is not just an occasion for old allies to renew vows of friendship. These two new, uncertain leaders need concrete achievements and not just gestures.

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This is a critical moment for journalism, particularly in the United States.

More than 40 years ago, the unmasking of the Watergate break-in inspired journalists around the world.

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Psychology is always part of tense negotiations. In her Lancaster House speech this week Theresa May sought to seize back the advantage before the real battles start at the end of March. She wanted Europe to know that Britain would not be coming to meetings on the defensive, cap in hand.

During the 40 minutes of her speech she managed to shift the balance of power a little. A few days before she spoke I had been in Brussels and had spoken to a very senior European figure.

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It is a curious moment in British politics. The government is facing the most important negotiations in over 50 years. The outcome will shape the future of the UK economy - but you would not necessarily know it.

The consumers - the voters - appear to be shrugging off the uncertainties, the unknowns and the warnings of future risks.

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2016 was the year of the unravelling. Norms were dispensed with. Old ideas were challenged and discarded. Our settled world was shaken and we became used to the shock of the new.

Since World War Two, and earlier, there was a consensus that trade was about much more than just economics. It was an instrument for peace. Reducing trade barriers sparked growth and prosperity. That consensus is creaking.

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The year ends with a Brexit puzzle: a multi-coloured cube that, however twisted and turned, defies easy solution.

Six months on from the UK referendum, the process of leaving the EU is enveloped by a cloud of unknowing.