Turning points in world affairs form flashbulb memories, vivid snapshots of the scene when we heard the news: declarations of war; assassinations; natural disasters. They form the album of shared memories that defines each generation.

On the November morning in 1990 when Margaret Thatcher resigned, I was at school. I can picture the very classroom. The teacher took the unprecedented step of wheeling in a TV so we could watch the Iron Lady’s momentous departure from Downing Street. I had no notion of what it was like to have a different prime minister. French friends say it was the same for them when François Mitterrand stood down in 1995, after 14 years in the Elysée palace. It took a while to get used to hearing the words “monsieur le president” in reference to a different face.

Merkel must have wondered what on earth had happened to Britain when a buffoon like Johnson became foreign secretary

And so there will be a generation of Germans who struggle to get their heads around the idea of politics without Angela Merkel. They don’t have to adjust overnight. Merkel has signalled that she will not seek re-election as leader of her Christian Democratic Union party – a role she has occupied since 2000. She has been chancellor since 2005 and can carry on in that post, but yesterday’s declaration effects a status shift from leader to caretaker. Merkel’s domestic position has been shaky since elections last year forced her into an unstable coalition with a debilitated Social Democratic party. That partnership elevated the far-right Alternative für Deutschland to the status of principal opposition party by default. Subsequent regional ballots have reinforced the sense of malaise in Germany’s political centre, as voters migrate towards the fringe. A poll in Hesse over the weekend was won by the CDU, but the party’s share dropped by more than 11 points. The SPD also shed support, while the Greens and AfD made significant gains.

Facebook Twitter Pinterest Prime minister Tony Blair and Angela Merkel outside No 10 on 24 November 2005, two days after Merkel became chancellor of Germany. Photograph: John D Mchugh/AFP/Getty Images

Germany is moving on from the Merkel era. The transition will be drawn out, but the confirmation is still a flashbulb moment across Europe. Length of service is only part of the story. Merkel has seen world leaders come and go. Tony Blair was her first British counterpart. She indulged David Cameron as the “naughty nephew” of whom she tried to make a responsible European. She warned him against trying to placate Eurosceptic backbenchers, correctly predicting that they would never be satisfied. She was apparently unimpressed when Theresa May wasted their first bilateral encounter in 2016, giving nothing away, reciting lines from a prepared script.

Merkel must have had occasion to wonder what on earth happened to Britain when a buffoon like Boris Johnson could become foreign secretary, and be replaced by Jeremy Hunt, a man who can glibly equate the EU and the USSR. Merkel’s childhood was spent in communist East Germany. She knows the difference between a union of free democracies and a prison state. Where, she must ask herself, did all the grown-ups go?

Meanwhile, Britain’s liberal internationalists admired Merkel’s principled embrace of Syrian refugees and marvelled at history’s capacity for irony: placing the torch of tolerance and good global governance in the hands of a German chancellor for safekeeping, and having her stand as cultural foil to a racist, demagogic ruler of the United States.

There is some simplistic mythologising in the admiration of Merkel as the anti-Trump figurehead for European civilisation. (Open-border generosity hasn’t done her much good in domestic politics). But the very existence of that hagiography expresses a powerful craving for stability, maturity and dignity in global affairs. The victory in Brazil’s presidential election of Jair Bolsonaro – an aggressive far-right authoritarian – tilts the global balance another few degrees against the rule of law and towards a doctrine of swaggering, might-is-right machismo. It might be coincidence that Bolsonaro enters on one side of the stage just as Merkel prepares her exit, but that doesn’t make the contrast less poignant.

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In Britain, these developments were submerged in coverage of the budget, although in years to come no one will be swapping stories of where they were the day Philip Hammond delivered his 2018 fiscal set-piece. The whole show is meaningless without clarity about the UK’s relationship with the rest of Europe. The chancellor pretended to know the trajectory of the economy despite not knowing the future terms of trade with Britain’s closest neighbours. The Labour party pretended to have better ideas, because that is what the opposition does on budget day. But Jeremy Corbyn cannot describe his preferred arrangement of relations with the EU, or indeed the rest of the world, in terms any more convincing than May.

The prime minister’s ambition has shrivelled to the hope that parliament can be intimidated into agreeing to whatever second-rate Brexit plan she can eke out of Brussels, for fear that something worse would emerge from the chaos of its rejection. The Labour leader’s strategy is to provoke that chaos in the hope that, somehow, power changes hands in the subsequent melee.

While this pantomime plays out, Britain is not a serious or even a capable actor on the global stage. It is a case study in political dysfunction, a circus to make populists and tyrants glad and an item on the list that makes responsible politicians in Europe and the US fret about the health of liberal democracy. That anxiety is stoked by the prospect of Merkel’s departure, even if it has felt inevitable for a while.

In volatile times she has served as the ambassador from a more stable era, recent enough that it feels still comforting. When she goes, that era is formally committed to memory, consigned to the past, and there opens up a terrible vacancy. It is a shaming fact that Britain is in no condition to supply a candidate to fill it.

• Rafael Behr is a Guardian columnist