Within an hour of the Berlin massacre, in which 12 people died and around 50 were wounded after a terrorist drove a truck into a Christmas market, a tweeting senior representative of the far-right Alternative for Deutschland (AfD) labelled those who died "Merkel's dead".

Presumably the tweet referred to German Chancellor Angela Merkel's decision in September last year to wave through to Germany tens of thousands of refugees, including many from war-ravaged Syria, stranded on a railway platform in Budapest and the so-called Balkan route to northern Europe.

I say "presumably" because the tweet made no reference to facts, indeed seemed to seek to deliberately avoid them (at the time, the truck terrorist's identity was unknown). But such is the demagogue's strategy of hard trading in the power of suggestion: facts, opinions, statistics and beliefs are to be treated and manipulated as one and the same.

For the record, AfD is the political party whose youthful leader Frauke Petry told a German newspaper at the height of the European refugee crisis that it was acceptable for police to fire on refugees entering the country. AfD board member Beatrix von Storch later added in a Facebook post that if necessary, women and children could also be fired upon.

We now know that Berlin truck terrorist Anis Amri was not a "refugee" but in Europe for many years, four in Sicilian jails. Eventually he arrived in Germany but in July 2015, so had nothing whatever do with Merkel's decision to open the borders.

Of course, initial fears that he might have are understandable - though that is something separate from seeking to exploit them.

Perhaps the most charitable interpretation of populism in Europe and the West is that, behind the slurs, sexism and race-kicking, it serves to call the political and media elite to account.

When AfD smears the German chancellor, it is reflecting deep anxiety about immigration to Germany.

To those still unhinged by Donald Trump's election and Brexit, his supporters reply that he has enabled a kind of democratic "outing", where atomised political debate is offered up in the language people actually use - or at least some people, mostly on social media.

That said, calling a billionaire businessman with luxury hotels, golf courses and a Boeing 757 with 24-carat gold fixtures an "anti-system" warrior of the working man is a bit of fantasy casting for all but the populist far right.

When Trump talks about building a new brand of Berlin Wall across the US-Mexican border, I think of those shot dead seeking to climb that earlier wall, but his supporters hear an expression of the need for better border security.

When Trump tweets after the Berlin attack that "the civilized world must change thinking!", we should presume he's translating anxiety about migration, militant Islam and the limits of what Austrian philosopher Karl Popper called the Open Society.

Certainly, the Amri case has highlighted deficits in European reporting procedures and in the prosecution and deportation of immigrants with criminal backgrounds. And what's left of the passport-free Schengen agreement enabled Amri's movement across at least three European countries.

Though as one German commentator put it: "Anyone who has ever lived in a system in which mines and barbed wire prevent travelling is well aware of the fact that freedom of movement is a constituent part of freedom."

The problem is that populism doesn't seek to explore options, instruct or inform, but to inflame and exploit. An exultant form of nationalism, or protectionism, or xenophobia is used to delegitimise representative democracy.

It borrows, unwittingly presumably, from the radical elements it claims to oppose; certainly, it helps generate the confusion, and so the weakness and uncertainty, that those radical elements seek to cultivate.

To borrow from French economist and historian Nicolas Baverez, it's not enough to denounce populism - one must seek to disarm its causes.

But I fear that listening to its impulses, dutifully seeking to understand its re-emergence, might fail to limit the damage it can do.

Democracy is inevitably, by definition perhaps, made vulnerable by its diversity, but we should be as vociferous in standing up for liberty, with the same energy and force of conviction, as those who oppose it.

This means identifying the incendiary comments of ideologues as such - it means calling a spade a spade.

As George Orwell warned us some time ago, "we have now sunk to a depth at which the restatement of the obvious is the first duty of intelligent men" - today living in Donald Trump's "civilised world".

Richard Ogier is an Australian journalist in Munich. He is a former press attache to the Australian embassy in Paris.