Central American migrants amassed on the US-Mexican border have shown the limits of the “deterrence” argument on migration variously used in Europe, Australia and the US, and it is that when governments show sympathy to asylum-seekers, migrant arrivals dramatically rise.

The false contention is that they not only invite the problem, they create it — effectively putting boats in the water, calling would-be wolves to the national gates (“stone cold criminals” and “drug dealers”, according to US president, Donald Trump).

Australia has used the argument to justify the punitive, cruel and deceitful “Pacific Solution”, that shunts asylum-seekers including poly-traumatised children into cramped and unhygienic centres for long periods on remote islands.

And it was widely deployed against German Chancellor Angela Merkel when she opened her arms to thousands of asylum-seekers congregated on a train platform in Budapest in 2015. A humanitarian catastrophe in Europe was narrowly avoided but instead of recognition for moral courage, Merkel was blamed for the crisis, ex-post facto — as if standing for a selfie in a Berlin refugee shelter triggered the surging millions fleeing the brutality of Syria.

The migrants now in Tijuana, mostly from Honduras, Guatemala and El Salvador, must know that the White House incumbent is an anti-immigrant crusader for “zero tolerance”, criminalising border-crossings and separating children from their parents. They probably also know that he uses race, as he does national origin; religion; one’s sexuality and able body (or not), like superiority tropes to sew division in an attempt to bring people ‘on side’ — including from groups he marginalises, in fact.

But none of this, not the sheer physical and emotional challenge, not Trump baring his teeth at the Midterms — not the tear gas — has stopped thousands of desperate people from making the long and arduous journey north.

And therein lies the rub.

As ever with refugees, the story has been one of suffering, of people leaping from bridges, of tearful parents losing children in the throng. Secondary but worth noting, is that Trump’s callous politicking evokes the syllogism made known by the British Yes Prime Minister television sitcom. If my dog has four legs, and my cat has four legs, therefore my dog is a cat. Honduras has a drug problem, Hondurans are the caravan, so Honduran drug dealers will descend on the US like rain.

It’s a nasty bit of nonsense in the face of an extremely complicated problem: mass migration, and it ought to repel Trump’s god-fearing base.

Seen from Munich, the caravan recalls the bedraggled humanity of the so-called Balkan route three years ago, when hundreds of thousands of asylum-seekers arrived from life-disfiguring conflicts in the Middle East, notably Syria, and specifically the 20,000 who arrived at Central Station from Budapest on the first weekend of September, 2015.

The caravan also reminds one of the general exploitation of the migrant in European public policy debate currently — on the political extremes, yes, but more worryingly on the mainstream right. We’ve seen it in France, more recently in Austria and Italy, and in two German regional elections last month, though there with a glimmer of hope because the opportunism in Bavaria was so blatant — the Premier referring to “asylum-tourism” — that the reactionary conservative campaign came a cropper.

In the US, Trump’s response has been to defend the use of tear gas on women and children; deploy the language of warfare against people still a month’s footslog from the US, and have border troops erect “beautiful barbed wire” — to see little kids impaled upon? He’s flagged cutting financial aid to Honduras, Guatemala and El Salvador, when it’s precisely aid that addresses the underlying causes of mass migration in the first place.

Such a hard-line on both development aid and border control does not stop mass migration — so much for the hoary old “deterrence” argument. But it does drive desperate asylum-seekers into the arms of people-smugglers. And it is they, of course, who are the true predatory wolves.