Attack will accelerate the rapidly declining popularity of Merkel
There can be few more quintessentially festive places than a Christmas market, a place decked out in tinsel and holly, where parents and children come to shop and congregate in preparation for one of the Christian calendar's most family orientated holidays.
Berlin's popular Christmas market at the Kaiser Wilhelm Memorial Church is just such a place - and that is precisely why, if the ramming of that market with an articulated truck is confirmed as a terrorist attack, it will resonate so deeply in Germany.
Inevitably, the sight of a lorry jammed into market has evoked memories of July's attack in Nice when a 19-tonne truck was used in a rampage through a similarly symbolic setting - in that case the annual Bastille Day parade on the sea front promenade.
Such attacks are calculated by Isil to cause maximum carnage and to sow the seeds of division in western societies: to pit Christians against Muslims, Europeans against those of Middle Eastern descent.
To that end, the terrorists - now under increasing threat in their bases in Syria and Iraq - have written in their propaganda magazines about trying to destroy what they call the "grey zone" that enables multicultural societies to co-exist, and to force both sides to choose between black and white.
It is for this reason that Angela Merkel, the German chancellor who opened Germany's door to nearly a million asylum seekers in 2015, will desperately want to resist any knee-jerk reaction to last night's attack, if that is what it turns out to be.
But equally, it is for this very same reason that the German chancellor, who will seek re-election for a fourth time next September, will be fearing the political fallout.
Although still popular by the standards of many leaders in Europe, Mrs Merkel has never been so vulnerable.
Already this year Germany has faced some smaller attacks - in July a 17-year-old Afghan refugee attacked passengers on a train before being shot dead - handing further ammunition to rising political forces on the German right. But nothing on this scale.
It is too early to know who was behind the wheel of the truck that rammed into the Berlin market last night, but if it turns out to be another asylum seeker who swept into Europe along the unpoliced Western Balkan route there are plenty in Germany waiting to capitalise.
This year Alternative for Germany (AfD) has scored a string of local election victories, at one point touching 15pc in the polls - a figure three times the minimum 5pc threshold that would give it seats in Bundestag. If it maintained that performance - and its anti-immigrant agenda feeds off terrorist incidents - they would become the first far-right party to achieve seats in the Germany's national parliament since the World War II. That in itself would not be enough to unseat Mrs Merkel, but it would continue the rapid erosion of her authority.
Mrs Merkel, ever the pragmatist, has already tacked to the right, pledging never to repeat her "open-door" refugee policy.
Her problem is that that particular horse may have already left the stable. (© Daily Telegraph, London)