Barack Obama’s presidency will be defined by his failure to face down Assad

The US president’s indifference to chemical warfare led to the trail of violence that reached as far as EuropeOn Friday, near Palmyra, 14 tanks and an anti-aircraft system were destroyed in an air strike on Isis. Palmyra recently fell to the jihadists after the Syrian regime and its allies diverted forces to Aleppo, leaving the ancient city under-defended.This was a repeat of events last year when, on the advice of the Iranian general Qassem Suleimani, the regime deployed troops away from