It will be called the great betrayal. And it was a long time coming. But the grim message from Washington to the anti-Assad fighters of southern Syria – that they could expect no help from the West in their further struggle against Assad’s regime or the Russians – will one day figure in the history books. It’s a turning point in the Syria war, a shameful betrayal if you happen to belong to the wreckage of the “Free Syrian Army” and its acolytes around the city of Deraa, and a further victory for the Assad regime in its ambition to retake all of rebel Syria.

Already Russian missiles and Syrian bombs are embracing the countryside south and east of Deraa and outside Quneitra and Sweida after the opposition fighters refused a negotiated peace last week. Refugees are again fleeing the towns. But the words of the American message to the fighters, seen by Reuters and so far not denied by the US, are both bleak and hopeless: “You should not base your decisions on the assumption or expectation of a military intervention by us … We in the United States government understand the difficult conditions you are facing and still advise the Russians and the Syrian regime not to undertake a military measure that violates the [de-escalation] zone.”

When Washington “understands the difficult conditions” its militia allies are facing and says it “advises” the Russians and Syrians not to violate a ceasefire – which was Moscow’s idea in the first place – you know that the Americans are pulling the carpet from beneath another set of allies.