‘They are concentration camps,’ Alexandria Ocasio-Cortez said of the immigration detention centres on the southern border of the US. Right-wingers angrily replied that she was either simply wrong, or making trivialising comparisons between mere brutal, dehumanising detention and the Nazi project of mass extermination. Not so, Ocasio-Cortez argued: concentration camps existed long before the death camps, and it’s an accurate term for the border facilities, which are characterised by the deliberate combination of extrajudicial internment, bureaucratised neglect and institutional cruelty.

She was right, though the camps’ defenders may have been relieved to be embroiled in an argument over terminology and historical propriety. It’s easier for the hairsprayed Lord Haw-Haws of Fox News to lambast a young socialist politician than to justify the cramped and freezing facilities where children sleep on concrete and are denied basic sanitary provisions, vulnerable to lice and infection. Carlos Hernandez Vásquez, a Guatemalan asylum seeker, died in a Texas holding facility in May, having been diagnosed with flu. He was 16 years old, and the fifth Guatemalan child to die in six months. The McAllen processing centre, where he had been held, is designed for 1500 people. In the week he died it held 2500, with sick detainees sleeping on floormats in an overflow tent.

The overcrowding is not unusual: Border Patrol facilities now operate at four times capacity, holding around 15,000 people; another 52,000 are detained by Immigration and Customs Enforcement. Lawyers who visit the camps return with stories of suicidal, self-injuring and traumatised children; older children are being used by the guards as substitute parents for toddlers. Last month, Senator Lindsey Graham proposed raising the detention period for minors – already often flouted in practice – from 20 to 100 days. Proposals for expanded detention facilities are careful to site them on federal land, inaccessible to state welfare checks, or look to the legal grey zone in Guantánamo, where Haitian migrants were detained in the 1990s.

However accurate AOC’s description, much of the moral weight behind the phrase ‘concentration camps’ comes from the collapse of its prehistory into the Holocaust; it’s hard not to flinch from any implied comparison. The policy of concentration or arbitrary detention, however barbaric, is different from the pursuit of mass extermination. The implied question is whether one can slide into the other. In two lectures collected in her last work, Mourning Becomes the Law (1996), derived in part from her experiences teaching and consulting for the Polish Commission on the Future of Auschwitz, Gillian Rose grapples with similar questions, arguing that this moral flinch comes from a desire to find a total break between our own political environment, our own habits of thought, and those of fascist Europe. ‘Never again’ may not be a historical imperative so much as an a priori claim about historical possibility. ‘We dare not understand,’ Rose writes, ‘because we fear that it may be all too understandable, all too continuous with what we are – human, all too human.’

Defenders of the Trump presidency have pointed to the camps’ antecedents under Obama, and ICE’s higher rate of deportation during his administration. Trump’s innovations have been in the realm of publicly displayed cruelty, from family separation to eruptions on Twitter, dangling threats of huge ICE raids to cow Democratic opponents. It is certainly possible to see this public cruelty as a qualitative break, but it also inherent in the border system itself.

The most striking recent precedent for Trump’s camps is the Maricopa County Sheriff’s Office under Joe Arpaio. An early Trump supporter and ardent believer in ‘birther’ conspiracy theories, ‘Sheriff Joe’ ran a jail he called ‘Tent City’ where inmates were exposed to Arizona’s baking daytime heat and freezing nights. He specialised in humiliation, and delighted in showing off his petty cruelties to the international media, giving inmates mouldy food or insufficient water in the desert heat. In private, among supporters, he boasted that he ran a concentration camp. Amnesty International condemned him; he doubled the press tours for his expanded facility. A DOJ investigation found him responsible for the most flagrant example of racial profiling in US history; a court eventually found him guilty of criminal contempt over related proceedings. Trump pardoned him.

The centrality of anti-migrant policy to Trump’s presidency, and the cruelty with which it is carried out, can tempt transatlantic observers into believing it is a uniquely American form of barbarism. But its continuity with policy elsewhere is striking: the third-party concentration camps run by Australia in Manus and Nauru, the miles of razor-wire along Hungary’s borders, the torture centres and slave markets of Libya to which desperate migrants trying to cross the Mediterranean are returned. Where Europe does not equal America, it exceeds it: Frontex and the vast Eurosur surveillance system, which would be the envy of US agencies, are politely overlooked by most Europeans.

Europe’s unwillingness to accept migrants increases the stress at its borders: Italy’s repugnant interior minister, Matteo Salvini, has built his career on anti-migrant populism, declaring war on ‘illegals’ and drafting a new law to fine NGOs thousands of euros for rescuing drowning migrants. But Salvini’s sense of grievance is also directed at, and enabled by, the EU’s Dublin Regulation, which requires people to apply for asylum in the country through which they enter the union. The closest the EU has come to dealing with the problem is a proposal to build detention centres in North Africa; the walled Spanish exclave cities of Ceuta and Melilla, where migrants risk injury and death to cross the border and claim asylum, offer a preview of their operation. The US is distinguished, if at all, only by the honesty of its cruelty, and the efficiency of the wolf-eyed Stephen Miller in extirpating all political objection from migration agencies.

Any movement to defend the rights of migrants and refugees faces three significant problems. The first is that the architecture of international obligation governing refugees’ rights and states’ obligations to them (the 1951 convention, drawn up in the wake of mass wartime displacement, and its 1967 protocol, which recognised its universal application) has had its foundations undermined by powerful states, which routinely flout its restrictions on refoulement.

The second is a perceived mismatch between ethical obligation and political calculation: it is assumed that voters will punish politicians who are seen to prioritise the needs of those outside the political community; individual states are disincentivised to take unilateral action by others’ unwillingness to co-operate, and only the strongest politicians (as Merkel did in 2015) can risk it.

The third, which grows out of the second, is the genuflection of social democratic parties before the claim that ethnic homogeneity and hostility to migration are immutable characteristics of the working class, and a tendency to ground defences of migration in contingent economic advantage for the receiving country. Lurking behind these is an intuition, rarely expressed, that prosperous welfare polities are fragile things, in terms of both domestic consent and global inequality – and they will face serious challenges in responding to the waves of climate refugees the 21st century will produce.

The late Michael Dummett, with rigorous philosophical radicalism, took seriously the rhetorical premise of human equality and rights to freedom as foundations for a defence of migration. He also argued that the duty of a state to aid refugees must entail a duty to allow people to claim that aid. Everything from ‘carrier liability’ – a US invention placing visa duties on airlines rather than the state – to government press releases emphasising anti-migrant policy can be understood as attempts to forestall those duties. It is this derogation in practice from the universal rhetoric of human rights that led the UN’s special rapporteur, Philip Alston, to warn that the coming century will see ‘climate apartheid’ and the disappearance of any shared sense of human obligation.

These are serious political problems that cannot be solved by slogan or willpower: the quiescence of the most pro-migrant Labour leadership in history suggests how intractable it is in the sphere of formal politics. The UK’s border regime has its own notorious, parochial cruelties – the ‘go home’ vans, the ‘hostile environment’, a network of detention centres and unlimited detention periods – but campaigns against them have been led by grassroots activists, NGOs and investigative journalists; Labour’s political commitments, though a vast improvement on the promises for migration controls that the previous leadership had carved into a rock, are only promises to tackle the worst excesses of an unjust system.

There are rays of hope: a jury wouldn’t convict an Arizona man who left water in the desert for migrants; Wayfair staff have walked out over the company’s agreement to supply the US border camps; there are protests in the UK against Yarl’s Wood; and an All Party Parliamentary Group on unlimited detention has been established. Writers on migration sometimes end their pieces by suggesting that the camps and detention centres prefigure a dangerous and authoritarian future; the truth is, with at least 18,000 drowned in the Mediterranean since 2014 and children dying in cages in America, that future is already here, it’s just unevenly distributed. The question is whether a different future is possible.