US military action against President Assad's forces in Syria seems imminent. President Trump told the Russians- Assad's military backers - to "get ready" by way of a tweet. A spiral of events which began with an alleged chemical weapons attack by the Syrian army is heading towards a dangerous confrontation between Washington and Moscow. HARDtalk’s Stephen Sackur speaks to Philip Gordon- Barak Obama's senior adviser on the Middle East in 2013 when Assad's use of chemical weapons came close to prompting a US military response. Did hesitation then sow the seeds of today's crisis?