Why does Bashar al-Assad keep doing it? On the evening of 7 April a chemical weapons attack hit Douma city, the largest and most symbolic area still controlled by rebels in eastern Ghouta – a region the size of Manchester. This pocket of resistance, which is located on the eastern outskirts of Damascus, has largely been retaken by Syrian regime forces in recent weeks, although rebels in some places have still refused to surrender. The latest attack killed at least 42 people and injured more than 500, according to reports from the Syrian American Medical Society, which runs medical facilities across the country. It estimates that most of the victims were women and children.

Numerous videos have captured the horrific aftermath of the attack, several of which show young children fighting for breath, suffocating and frothing at the mouth. Images like this have become far too common in the conflict. Apologists for Assad have claimed that jihadists rather than the regime itself might be responsible for the horrendous attack. The Russian foreign minister Sergei Lavrov said no evidence had been found of a chemical attack in Douma. After all, what does the regime have to gain from such an attack when Assad is winning the war that has raged on for seven years?

Pro-government forces, backed by Russia and Iran, have driven rebels from eastern Ghouta and have greater control over the rest of the country than at any other point since the Syrian crisis began in March 2011. Just when the tyrannical triumvirate of Assad-Putin-Khamenei has momentum and Donald Trump announces he wants American forces to leave Syria altogether, this attack happens. Why would the regime do it?

Should we need any more evidence, the Assad regime does not operate within the constraints of conventional political actions, as understood in the West. It is worth remembering that the sarin gas attack of 2013 in Ghouta brought no decisive military benefit for Assad and risked forcing the Obama administration to intervene in accordance with the so-called red line it had drawn against the use of chemical weapons.

In any event, the use of chemical weapons has become far more widespread than is often recognised. Since they were first deployed in the war in December 2012, the Syrian Network for Human Rights has documented 213 subsequent uses. That figure is broadly endorsed by the Syrian American Medical Society and the White Helmets, an aid agency working as first responders in rebel-held territories. Taken as an average, that is approximately three such attacks a month.

The devil is in the detail. There are, of course, a range of different chemical weapons available to the regime. The attacks that attract most attention are those with a significant death toll, or in which women and children are the main victims. The regime typically deploys chlorine through barrel bombs or rockets, which impact the immediate area in which a device falls but are generally not as lethal as other types of chemical weapons. The death toll might not be as high as a result. But the utility of chlorine lies in the psychological fear it spreads on the ground. Greater lethality typically arises from sarin attacks, of which there have been a number in eastern Ghouta.

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In other words, the regime is deploying these weapons consistently, deliberately, and with a conscious consideration of their qualitative effects. Assad has not simply eroded what academics call “the chemical weapons taboo”; he has shattered it. And his confidence has returned, especially compared to the high watermark of the war in 2014-15, when his authority had crumbled. Kurds dominated the north-east of Syria, while broader parts of the east had fallen to Islamic State. Meanwhile, an alphabet soup of various militias – jihadist and otherwise – rampaged across northern and southern parts of the country. Assad’s meaningful control only really extended across a small sliver of land from Damascus in the south through to his coastal redoubt of Latakia.

The intervention of proxy Shia militias from Hezbollah and Iran helped stop the rot, but it was the Russians who decisively tipped the balance in the regime’s favour. Just consider the carefully choreographed absurdity of Assad’s recent visit to newly reclaimed parts of eastern Ghouta for Syrian state television. He appears relaxed, wearing an open collared shirt, and drives a modest Honda Civic to the frontlines to congratulate his men. He speaks to the camera throughout, one hand on the wheel; the other pirouetting through the air, with blithe indifference to the catastrophic human suffering involved in his campaign to retake the area.

For a leader who will have been anxious about meeting a similar fate to Muammar Gaddafi in Libya, Assad cannot but help treat himself to an early victory lap. More importantly, he is no longer thinking just about winning the war, but about setting the terms for a peace in which his regime will aim to drive its advantage home for the coming decades.

When Assad arrived in Ghouta, his loyalist apparatchiks pumped their rifles into the air, triumphantly chanting “with our souls, with our blood, we will sacrifice ourselves for you”. Behind them lay a barren wasteland of destruction, in a province where an estimated two million people once lived.

What the regime desperately wants Syrians to understand is the continued and future cost of their disobedience. The message is clear: defy Assad, and this is what will become of your homes and neighbourhoods.

These are tried and tested methods for Syria’s Ba’athists who have been obsessed with their own survival since Bashar al-Assad’s farther, Hafez, led a coup d’état in 1970, becoming president the following year. Opposition to his regime intensified after Syrian forces invaded Lebanon in 1976, giving rise to a low-level insurgency led by the Muslim Brotherhood. Pockets of unrest developed sporadically, in areas such as Jisr al-Shughour (located in the western part of Idlib province, close to the border with Turkey, which is rebel-held today), and in districts of Aleppo such as al-Masharqah and Bustan al-Qasr.

These events culminated in a stand-off in the city of Hama in February 1982, resulting in a month-long siege during which an estimated 25,000 people were killed (estimates on the exact death toll vary between 4,000 and 40,000, although 25,000 appears most accurate based on academic accounts of the massacre).

For a regime that has traded in carefully calculated and strategically-minded repression since its inception, the lessons of the Hama massacre have not been forgotten. The crackdown delivered almost immediate results. By the middle of 1982, the opposition was battered and beaten.

Bashar al-Assad tried similar tactics during the early phases of the Syrian uprising, but the approach backfired. When his forces struggled to contain protests across the country, they concentrated their rage on Baba Amr, a neighbourhood in Homs widely regarded as the epicentre of the revolution. The area was besieged and then shelled without remorse. Among the many victims were Marie Colvin, the celebrated Sunday Times reporter, and Rémi Ochlik, a French photojournalist, who both died in February 2012. Hours before her death, Colvin had spoken to CNN about the regime’s indiscriminate violence. “[There] are 28,000 civilians, men, women and children, hiding, being shelled, defenceless,” she said. “The Syrian Army is simply shelling a city of cold, starving civilians.”

In 2012 Assad could not replicate the success of his father, but he has since revived those methods in more fortuitous circumstances. The changed realities of the Syrian war today allow the regime to deploy brutal force with the hope of shunting people back into obsequiousness. Chemical weapons are a deliberate part of that calculus.

Syrian children look out of the broken window of a bus carrying civilians from war-ravaged eastern Ghouta on 10 April. Credit: Getty

So how can we expect the West to respond? At one level, President Trump’s apparent willingness to take action in the wake of the latest atrocity – he tweeted that there would be a “big price” to pay and has vowed a quick and “forceful” response – is intended to distinguish him, once again, from his predecessor. The disintegration of Syria since Barack Obama’s failure to enforce his own so-called red line leaves a stain on his administration. A self-described tragic realist, Obama, who opposed the Iraq War, was deeply reluctant to be drawn into Syria. As a consequence, he has a poorer record on the defining humanitarian crisis of our times than his boorish successor. In 2012, when the Syrian regime first used chemical weapons, there were some who lauded Obama for avoiding the rush to war and instead negotiating a deal with the Russians, by which these stockpiles were supposed to have been removed from the country. How hollow that argument looks now.

In the case of Trump, however, any credit he gets for apparently having a lower threshold for tolerating Assad’s most egregious crimes must be considerably hedged. On 7 April last year the Trump administration struck the Shayrat Airbase in Syria – the site from which a sarin weapons attack had been launched against the residents of Khan Sheikhoun in Idlib province – with 59 Tomahawk cruise missiles. Trump claimed a feeling of revulsion at the targeting of women and children. He has similarly condemned the latest outrage in Douma as “mindless” and “sick”.

But the president is also guilty of incoherence and inconsistency, with more than a dash of cynicism in his own response. When the Obama administration was agonising over whether to intervene militarily against the Assad regime in 2013, Trump then took to Twitter and urged him not to: “There is no upside and tremendous downside,” he said, “Save your ‘powder’ for another (and more important) day!”

Minds can change, of course, and perhaps Trump has decided that the time to reach for American powder has arrived once again. Yet the attention that he has given the Syrian war has been no more than fleeting and episodic, largely in tow to the news cycle. While one may reasonably expect an attention deficit from this president, the failure to follow up on his own red lines with a sustained diplomatic strategy has not made for a successful deterrent. More broadly, the continued failure to fill key posts in the state department, where morale has never been lower, has left a vacuum in American diplomacy. After a single display of military power in April last year, the broader Syrian war slipped off the agenda as attention moved back to the campaign against Islamic State, which appeals much more to Trump’s base instincts.

In recent weeks, the Trump administration had made bold, triumphalist, statements to the effect that the threat from Islamic State was all but eradicated. Just days before the last chemical attack, there was a further announcement that the administration was considering extracting itself from Syria altogether. Most likely, Trump’s decision to order an American withdrawal represented several calculations operating together. First, with mid-term elections looming, he is keen to demonstrate a foreign policy success and the fulfilment of a campaign promise to destroy Islamic State. By declaring “mission accomplished” he meets this need. Second, more broadly, Trump seems to have revived his previous hostility to what some describe as the “globalist” faction within the national security establishment. The ousting of Rex Tillerson as secretary of state and HR McMaster as national security adviser is said to reflect the president’s mounting frustration that he was being thwarted by underlings. Defence secretary James Mattis is the last of the so-called adults in the room.

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Future historians might see this as the moment that something resembling a Trump doctrine – or at least a set of identifiable instincts – began to take shape, however half-formed. Allergic as he is to putting troops on the ground – or pursuing anything resembling a conventional humanitarian intervention – Trump also has an instinctive aversion to anything that seems to throw dust in the eyes of America. The threshold for significant troop deployments (as favoured by McMaster in Afghanistan and Syria, for example) is extremely high. But there is an alternative tariff in operation, from North Korea to the Middle East.

The reasoning goes something like this: the mistakes of Bush and Obama are to be avoided; but there remains a willingness to assert American muscle and threaten punitive action. This mechanism is not enacted in a traditional defence of the international rules-based order but emanates from a more primal reflex drawing on a sense of prestige and power. Thus, Trump’s tweets veer from regret that his conciliation with Russia has been frustrated - in his eyes by the Russia investigation - to the bombastic warning that missiles are on their way to Syria. “Get ready Russia, because they will be coming, nice and new and 'smart'!"

This is where the blunt wedge that is John Bolton, McMaster’s replacement as national security adviser, comes in. It was Bolton’s appearances on Fox News, defending the president’s agenda rather than trying to soften its edges, that are said to have attracted Trump to this long-time Republican hawk. If Bolton is distinguished by one thing, it is his conviction that the US has been too cautious in deploying force to uphold American interests and security.

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The conundrum that will have faced Bolton on his first day in office is one for which, in his own estimation, he is perfectly suited. Like the president, he will feel compelled to show American strength. Herein lies the danger of a half-baked policy. Trump’s last foray into this conflict, the cruise missile strikes against Syrian targets in April 2017, did not achieve its desired effect. If another largely symbolic gesture is followed by a further degradation of international chemical weapons control, it will continue a steady diminution of American power that can be traced back to at least 2003. As for those crowing that the world’s policeman had become a cowboy, too unilateral in its actions, the consequences of an anarchic international order going largely unchecked are there for all to see.

At the time of the April 2017 strike, the administration was eager to minimise risk to citizens of other countries – particularly Russian forces – who were known to be operating in the area. Almost exactly a year later, as it debates the details of its likely response, some of the dilemmas will be the same. There is the question of whether to focus simply on chemical weapons facilities in similarly limited strikes or whether a more substantive punitive approach is adopted to damage the Syrian regime while potentially raising the prospect of further reprisals.

And the geopolitical context is considerably altered since last year. This might change the calculations of the US administration and those – particularly France and Britain – who have signalled their willingness to act in concert. First, Islamic State is much diminished. The old Hobson’s choice – always a false one, successfully propagated by Assad – that clipping the Syrian regime’s wings meant helping the caliphate – no longer carries the same weight. Second, the notion that Russia could be a responsible partner – as Obama had hoped in 2013 – has been severely undermined.

Indeed, what was different about Trump’s initial response to the most recent chemical attack in Douma was his willingness to extend his opprobrium to Russia and President Putin, as well as Iran. The desire to push back against or thwart the expansion of Iranian influence across the Middle East has been one of the administration’s most consistent policies; a sentiment that will be further burnished by Bolton’s arrival in the White House.

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There is a growing feeling among leading politicians in the West that, after a string of tactical victories, Putin overstepped the mark in the Skripal affair in Salisbury. Having been met with an unexpectedly robust response from Britain, the US and a number of European states, there is reason to think that he has been put on the back foot. It may well be that the Trump administration – encouraged by a proactive President Macron and the British government – sees a moment to drive this advantage home. Momentarily, at least, the proliferation and increased use of chemical weapons, from Salisbury to Syria, has provided the Western alliance with a much-needed sense of common purpose.

Once again, Syria has proven to be the problem that cannot be ignored, however much the West has tried. The ugly status quo engineered at great human cost by the Syrian regime – with the support of Russia and Iran – has been disturbed. Assad has brazenly continued to deploy chemical weapons on a regular basis with no great fear of any serious costs. For many years, the West has pursued diplomacy neutered by the absence of any willingness to deploy force; today, the danger is of a reflexive use of arms without any considered diplomatic strategy. These whimsical and fleeting fits of moral panic directed towards the defining crisis of our generation do little to defuse a febrile international climate.

John Bew and Shiraz Maher are academics in the Department of War Studies, King’s College London, and New Statesman contributing writers