If the Kurds cannot guard the ISIS captives, then who will? (Photo by Burak Kara/Getty Images)
One of the more ludicrous suggestions to have been made during Turkey's military offensive against the Syrian Kurds is that, in return for Washington's approval, Turkish President Recep Tayyip Erdogan would take responsibility for the estimated 90,000 ISIS fighters and their dependents, currently languishing in Kurdish-controlled detention centres.
It is one of the worst kept secrets in Western intelligence circles that, for long periods during the brutal Syrian conflict, Mr Erdogan's regime supported a number of groups that enjoyed close affiliation with ISIS, as well as other Islamist terror groups such as Al-Qaeda.
It is, therefore, the epitome of hypocrisy for Mr Erdogan to offer to take responsibility for the ISIS fighters being held in Kurdish-run detention camps such as the al-Hol complex in eastern Syria. If that really were to happen, and the ISIS captives were repatriated to Turkey, it would, for some, be more like a homecoming.
There is, fortunately, only a remote likelihood that captured ISIS fighters will be making their way to Turkey anytime soon, for most of the detention camps are located well away from the 30 km buffer zone on Syria's northern border, the main target of the Turkish offensive.
The far more worrying prospect is that the captives may be able to escape, and return to the ranks of ISIS's terrorist infrastructure because the Kurdish-led Syrian Democratic Forces (SDF), which are currently responsible for holding them, will no longer have either the manpower or the will to continue running the numerous detention facilities in which the captives are being held.
Prior to Turkey launching its offensive, which bears the unlikely codename "Operation Peace Spring", Mazlum Abdi, the commander of the Kurdish-led Syrian Democratic Forces, announced that some of his forces tasked with securing the ISIS prisoners would need to be redeployed to the border to do battle with the Turkish military.
If the Kurds cannot guard the ISIS captives, then who will?
That so little progress has been made in dealing with the ISIS fighters, many of whom have now been in detention for more than a year, is down to the failure of the West, and Europe in particular, to acknowledge their responsibilities.
The ISIS caliphate might no longer exist, but the terrorist organisation itself still continues to operate. Indeed, the latest intelligence assessments are that ISIS is regrouping in countries such as Syria, Iraq, Afghanistan and Yemen, with the aim of launching a fresh wave of terror attacks against Western targets.
ISIS's ability to launch such attacks, moreover, will be greatly enhanced if experienced fighters currently being held in Kurdish-run detention camps are able to make good their escape and return to their former terrorist associates.
Of particular concern for Western intelligence officials is the fate of the estimated 2,500 foreign fighters - the majority of them from European countries such as Britain, France and Germany - who have been abandoned by their home countries.
European officials have refused to repatriate them because of the continuing threat they would pose to the security of their citizens. Europe's failure to accept responsibility for the conduct of their own nationals, however, has caused friction with the Trump administration, which has called repeatedly on Europe to act.
Now President Trump's own precipitate actions in allowing the Kurds to launch their offensive in northern Syria could have its own disastrous implications for the fate of the ISIS fighters.
The willingness of the Kurds to continue guarding their ISIS captives will inevitably be diminished as a result of the betrayal they believe they have suffered at Washington's hands.
Consequently, serious consideration must now be given to the possibility that some of the ISIS fighters will ultimately be able to make good their escape and rejoin ISIS.
The US has already acted to make sure that some of the more notorious captives, such as the two British jihadis known as the "Beatles" who tortured and murdered Western hostages, have been taken into American custody as a precaution.
Mr Trump has made it clear, though, that the US is not prepared to accept responsibility for all the captives, especially those who originate from Europe.
So that leaves tens of thousands of ISIS fighters stranded in a diplomatic no-man's land, from whence they may well be able to make good their escape.
If this happens, then Mr Trump's claim that the war against ISIS is over may prove to be short-lived.
Con Coughlin is the Telegraph's Defence and Foreign Affairs Editor and a Distinguished Senior Fellow at Gatestone Institute.