President Recep Tayyip Erdoğan has already threatened to send Turkey’s army over the border into Syria, with the twin aims of preventing the defeat of his rebel allies and carving out a buffer zone along the frontier. Suppose Mr Erdoğan were to go ahead and deploy his troops in Syria: the greatest risk would be that Russia responds with air strikes against Turkish forces.

How plausible is the following scenario? After Russia bombs Turkish troops inside Syria, Mr Erdoğan deploys his air force to protect his ground units – and three Russian MiGs are shot down. Russia immediately retaliates by striking the air base inside Turkey used by the jets that destroyed the MiGs.

After one of his air force bases is pulverised by the Kremlin’s bombs, Mr Erdoğan then declares that Turkey has suffered aggression from Russia. He demands the help of his allies in accordance with Article V of the North Atlantic Treaty, which states that an “armed attack against one” Nato member “shall be considered an attack against them all”.

Put bluntly, Mr Erdoğan could invite us to choose between going to war with Russia, or shredding the credibility of the collective security guarantee that serves as the bedrock of Nato. How would we respond?