Australia has been detaining refugees on Manus Island and Nauru, with only a brief interruption, for over fifteen years. The conditions of this detention have never been anything but deeply inhumane, so it’s been a long time coming, but our political leaders are finally starting to feel the heat. Between The Guardian’s Nauru Files, the groundswell of support – including from state politicians – for movements #LetThemStay and #BringThemHere, and the steady rhythm of condemnations from various branches of the UN, the pressure is building. Malcolm Turnbull would love to empty the detention centres and clear the issue from his agenda. The ALP, too, would be greatly calmed by the end of a policy whose brutality has intensely strained the party’s unity.

So there’s an appetite to get these people – roughly two thousand of them – out of detention. Our Prime Minister has decided that this should be done by giving refugees currently in Costa Rica the right to live in Australia – something they have not previously expressed any desire to have – and shipping those who wanted to come here to the United States instead. It’s a contorted policy. But it’s not a crazy one. This refugee swap deal is the inevitable result of trying to fit the humanitarian goal of ending offshore detention within the bipartisan framework of cruelty that has come to structure our asylum policy.

The core of the difficulty is a genuine policy challenge that governments across the world are forced to confront. Practically all countries recognise that they have obligations to help refugees, including by giving residence to at least some of them. But they also want to discourage ‘spontaneous arrival’ by people who have not been vetted and who are forced to use the services of smugglers. This kind of migration tends to be exploitative and often to put refugees’ lives at risk. We’re familiar with politicians’ desire to stop asylum seekers in leaky boats drowning in the Indian Ocean; the same problem arises in the Mediterranean Sea, the harsh deserts of the southern US, and the jungles of Brazil. The aim of designing a policy which doesn’t encourage more refugees to put themselves in life-threatening situations is a real and important one – even if politicians tackling it inevitably have mixed motives, and use the humanitarian rhetoric as a screen for their more basic desire to stop large numbers of migrants arriving at their borders.

There are two broad ways of reducing how many people make dangerous journeys to Australia. One is to slash the rewards to that decision, by requiring a period of detention for those who arrive irregularly or refusing to grant them permanent refugee status. The other is to make the option of regularised migration more attractive and accessible. Brazil, facing the deaths of more and more Haitians migrating irregularly through the jungle, opened a special centre in Port-au-Prince to receive applications for a new class of visa for Haitians. Italy has started to fly Syrian refugees directly from Lebanon, to undercut the need for smugglers.

Most policy arrangements combine a little of both elements. The EU’s much-maligned deal with Turkey, for instance, involved summary deportation of migrants arriving irregularly by boat alongside an undertaking to expand formalised refugee admissions for those in Turkey. But Australia has bet the house on the first option: pure deterrence. Every policy decision Australia has made since introducing mandatory detention for boat arrivals in 1992 – apart from the few months in 2008 between Labor’s dismantling of the Pacific Solution and its freezing of asylum claims from Sri Lanka and Afghanistan – has been targeted at making the lives of boat arrivals worse and, ultimately, at barring them from ever getting any benefits from Australia.

As domestic politics, too, both parties have locked on to the rhetoric that we not only have to be cruel to be kind, but that the slightest actual kindness would be unforgivable. This is the context to a series of otherwise baffling policy decisions: not to let refugees be resettled in New Zealand (since they might, some years later, get a New Zealand passport and come to live in Australia), and later the even more sweeping and ridiculous decision to block any boat arrival from even visiting Australia at any point in the future.

Malcolm Turnbull’s problem is that while public pressure, the moderate wing of his party and perhaps his own instincts all push in the direction of ending detention, he’s constrained by our past policy choices from taking the obvious solution. It would be extremely easy to bring all the refugees in detention to Australia: the government has committed to taking ten times as many people ever year. It wouldn’t even necessarily mean abandoning boat turnbacks, which appear to be the measure that really succeeds at discouraging irregular journeys. But doing this would be totally at odds with the government’s stated policy, and would undermine what has been for twenty-five years the cruel heart of our approach to refugees.

If refugees are going to get out of detention, our politicians have concluded, they need to be sent far away and never allowed to come back. That’s why the PM turned to Barack Obama to solve this problem for him. But Obama is gone; in his place is a man who’s tweeted angrily that the swap arrangement is a ‘dumb deal’. The worst part is that he’s not wrong. The refugees Australia will take in return are not currently in the United States or even under its authority. Having more refugees safely resettled and fewer in camps in Costa Rica was, for President Obama, an outcome worth making a deal for. But if President Trump doesn’t see it that way, there’s no real way to convince him.

Turnbull reportedly, in that infamous phone call, said that a businessman should understand that deals have to be honoured. That does not appear to be a lesson that’s played a major part in Trump’s business career.

But we – not to mention the refugees – are reduced to crossing our fingers that it’ll stick. Here, if anyone needed one, is another unforgivable consequence of Australia’s bipartisan refugee policy. We are not only unconscionably cruel ourselves. We’ve created a situation where refugees’ only hope for escaping our cruelty is an act of selfless mercy from Donald J Trump.