Forget for a moment the manner in which Donald Trump has sold out the Kurds during an admiring late-night call with Recep Tayyip Erdogan, Turkey’s strongman; his US troop withdrawal, which caught White House advisers by surprise: the bombastic tweets that followed. All these were vintage Mr Trump. But we should not let the noise obscure the signal. America has been trying to extricate itself from the Middle East for years. Mr Trump is only following in the footsteps of Barack Obama.

It used to be said it was better to be Britain’s enemy than its friend; Britain made deals with its enemies and betrayed its friends. The Kurds might feel the same way about the US. As long ago as 1975, after Washington withdrew CIA support from an Iraqi Kurd uprising, Henry Kissinger said: “F**k the Kurds if they can’t take a joke.” Mr Trump’s decision to abandon America’s most important ally in Syria is reckless — not least because it opens the way for an Isis resurgence. But his betrayal is hardly original.

The difference is that the US is now paying a higher price for its mistakes. Mr Trump’s come in two forms. The first mistake is the way in which he makes them. It is one thing to catch your allies by surprise. It is another to wrongfoot your own staff. That produces confusion and demoralisation. Has Mr Trump given Mr Erdogan the green light to squash the Syrian Kurds? Nobody working for Mr Trump knows because he keeps contradicting himself. Mr Erdogan is probing the answer to that question.