Then, in August 2013 Assad’s regime, then two years into the civil war, attacked the Damascus suburb of Ghouta with sarin gas, killing more than 1400 civilians. The secretary of state John Kerry responded with a furious speech. “As previous storms in history have gathered, when unspeakable crimes were within our power to stop them, we have been warned against the temptations of looking the other way,” he said. “History is full of leaders who have warned against inaction, indifference, and especially against silence when it mattered most.” Loading Replay Replay video Play video Play video He noted also that America’s credibility rested upon its willingness to take action against Assad. “It is directly related to our credibility and whether countries still believe the United States when it says something. They are watching to see if Syria can get away with it, because then maybe they too can put the world at greater risk.” It appeared that Kerry did not doubt that Obama would enforce the red line, and soon Obama would reinforce that perception with his own statement from the White House. “It’s important for us to recognise that when over 1000 people are killed, including hundreds of innocent children, through the use of a weapon that 98 or 99 per cent of humanity says should not be used even in war, and there is no action, then we’re sending a signal that that international norm doesn’t mean much. And that is a danger to our national security,” he said.

But in the days after the statement Obama softened. According to Jeffrey Goldberg’s essay on the period in The Atlantic magazine Obama had come to view a military strike unsanctioned by either international law or Congress - and without popular support from the American people - as a mistake. Since then other critics have noted that by then his administration had already begun to focus on the Iran nuclear deal, and Iran backed Assad. Either way, Obama’s concerns were compounded when British parliament failed to give David Cameron its support for an attack. Further, Obama feared that any strike on chemical stockpiles might release plumes of lethal chemicals, killing even more civilians. To the dismay of many – including allies and senior voices in his administration – he backed down, delaying any action by asking Congress to authorise the use of force. That was when Vladimir Putin – ally to both Iran and Syria – stepped in. At his instigation and with his aid America and Russia engineered a deal whereby Assad would agree to surrender chemical weapons stockpiles for destruction. Supporters cheered the deal as a victory for peaceful pragmatism over force, critics viewed it as a surrender of American authority. Loading Russia, it appears, took it as a signal that it could fill an American void in Syria. In February 2015 the Russian parliament sanctioned its own use of military action in parliament, and soon its forces were targeting both rebels supported by the US as well as members of ISIS in support of Assad, changing the course of the war. Any hope of a regime change backed by the west vanished.

Then in 2017, two months after Donald Trump’s inauguration, a further 74 people were killed in a rebel-held district by chemical weapons unleashed in a Syrian government airstrike. A couple of short years after crafting a deal to have Assad surrender his chemical weapons, Putin was offering him protection as he deployed them again. Two days after the attack Trump ordered a missile strike, unleashing 59 cruise missiles at the airbase from the which the chemical attack had been launched. “It is in this vital national security interest of the United States to prevent and deter the spread and use of deadly chemical weapons," he said at the time. The attack was unilateral, but done after consultation with – and the support of – American allies. Russia described the strike as an act of aggression which “substantially impaired” relations between the two powers. Missiles streak across the Damascus skyline as the U.S. launches an attack on Syria targeting different parts of the capital. Credit:HASSAN AMMAR

Today relations between the two nations are even worse, both despite and because of the evidence that Russia meddled in the US election in an effort to support Trump’s campaign. While Trump has failed to personally condemn the Russian actions in the election – or the recent use of a nerve agent in England – the broader machinery of the US government has responded, most recently with the expulsions of diplomats. Some analysts have fretted that we are veering into Cold War without any of the established mechanisms for deconfliction and back-channel communication in place. The difficult – even dangerous – relationship between the two powers has made military calculous behind the strikes even more complicated. To demonstrate to Syria, Russia and Iran that the goal of the attack was to deter the regime from using illegal weapons, the strikes needed to be confined to targets related to the use of the weapons. Yet to achieve deterrence they also needed to be broader and more destructive than the 2017 strikes. By necessity then the targets included not only airfields, but sites thought to have been used for the development and storage of Assad’s chemical stockpile. This increased the risk of casualties among both civilians and Russians, and in turn the risk of escalation. Loading

The US Secretary of Defence, Jim Mattis, emphasised to the media after the attack, that planners did all they could to avoid such casualties, but he also said Russia was not notified of the attack beforehand. It is also significant that the attack was conducted in conjunction with Britain and France, signalling to Syria an international resolve that the use of chemical weapons will not be tolerated, and to Russia that the western order might be frayed, but is not toothless. It is not yet clear how the strike will leave relations between the US and its western allies and Russia. In her statement on the attack the British leader Theresa May was careful to make it clear that the intent of the attack was specific and limited. "We cannot allow the use of chemical weapons to become normalised within Syria, on the streets of the UK or anywhere else in our world," she said. "This is not about intervening in a civil war. It is not about a regime change.