It is unclear whether Turkey has the will or capacity to take over detention camps

In early 2015, as Islamic State trampled over armies of the Middle East and menaced the west, the US turned to the Kurds for help. It was a familiar call, having been repeated over the decades whenever Washington needed a friend in the region. The outcome has been similar too.

Four years on, the people who helped safeguard the global order have been abandoned by the US on the eve of a Turkish push into Kurdish lands across north-eastern Syria. Betrayal has been an enduring theme whenever the US and the Kurds have partnered, but never before as nakedly as this.

As US armour and troops started to leave the region on Monday, a frantic Kurdish leadership was demanding explanations and readying for an invasion that could change the map of the region and prove hugely consequential in other ways too, including undermining the security gains achieved in the war on Isis.

Since the battlefield victory, Syrian Kurds have swapped roles from fighters to jailers, detaining 90,000 suspected Isis supporters in four camps across the province. Guards remained loyal to the cause on the promise of ongoing patronage from Washington. They have far less incentive to do so now.

European states, deeply invested in what happens to the Isis camps, were blindsided by Trump’s announcement that Turkey would take control of them and sceptical that Ankara has either the will or capacity to do such a thing.

For its part, Ankara also appears to be surprised. The site of one camp, al-Hol, is not on maps it has prepared for its operation. Inheriting a headache on this scale seems to be part of a quid pro quo imposed on Recep Tayyip Erdoğan. A state dinner at the White House may well hinge on him agreeing.

Among the camp detainees are hard-wired ideologues who would be central to an Isis resurgence if given the chance. The spectre of a jihadist juggernaut once again roaming the plains of Iraq and Syria after using captivity to regroup – think the US-run detention centres in Iraq writ large – now hangs heavy over a region still grappling with the seismic regional power shifts that have defined Trump’s three turbulent years in office.

The abandonment of the Kurds is perhaps the most impactful of all. The debt owed to Kurdish forces is acknowledged by western security partners who realise Isis remains unfinished business. Trump’s US had found itself atop a world order it no longer wanted to lead and, more consequentially, no longer seemed to believe in. In the eyes of some bewildered regional allies, Iraq and Saudi Arabia in particular, the US has nothing left to offer but a chequebook.

Trump’s transactional worldview offers no place for history or morality. His ruthless short-term realism ignores the fact that the regional interests he does want to secure – containing Iran and securing Israel – are jeopardised by such a blatant betrayal.

For all the US president’s talk of taking on Iran, the Iranian attack on Saudi Arabia’s oil supply last month received no response from the US and has instead sparked a detente between Riyadh and Tehran that will inevitably lead to new trade openings and puncture US efforts to crush Iran’s economy.

When Trump first flagged a withdrawal from north-east Syria last December, his advisers were able to turn him around, partly by explaining that it would give Iran unfettered access in the province and make a coveted pathway to the Mediterranean Sea an easier bet. That logic stands 10 months on and has been reaffirmed by Iran’s activities near the Syrian border and in the Syrian port of Latakia.

Serving US interests is hardly a Kurdish priority now. Instead, allying with the Syrian regime in Damascus to ward off the Turks seems to be one of the few ploys open to Kurdish leaders, who would struggle to combat a full-scale Turkish invasion.

The prize for Turkey is significant: moving Kurds away from nearly the full length of the border and scaling back the gains made over the last six years by its arch-foe, the Kurdistan Workers’ party (PKK), which dominates administrative positions in the region.

This would be a triumph for Erdoğan, who throughout the war against Isis prioritised Ankara’s enmity with the PKK over that with the jihadists – a stance that drew US distrust. In Turkey’s eyes, the US had partnered with its worst enemy, claiming a false distinction between local Kurds and the PKK itself, forcing it to look elsewhere for friends.

Whether Turkey has a new friend in Trump will remain an open question. Whether the Kurds can trust the US has already been answered. Vanquished yet again, the Kurds must be wondering what they need to do to secure any sort of loyalty.