On 21 August 2013, at least 1,400 Syrians, including hundreds of children, were killed in Ghouta, east of Damascus. It was two-and-half years since the Arab spring uprising had begun against Bashar al-Assad. Regime forces used sarin, an internationally banned nerve agent, to target an opposition stronghold. And thereby hangs quite a tale. Barack Obama had already called on Assad “to step aside” and warned in 2012 that the use of chemical weapons would be crossing a “red line” – which would warrant military intervention. But the Democrat in the White House failed to carry out his threat, which was initially supported by allies, including Britain. Obama ended up welcoming an offer from Vladimir Putin to deal with this problem. Joby Warrick, a Washington Post journalist, and the author of a Pulitzer prize-winning book about Isis, has produced another highly readable and well-sourced work, a bleak but real-life thriller. Its characters include ordinary Syrians, spies, diplomats, UN experts and Americans who worked hard to destroy Assad’s chemical weapons arsenal, only to discover that they had not completed their task. Obama, of course, has had a good past four years, his two presidential terms elevated to near perfection by the intolerably divisive and self-interested Make America Great Again antics of Donald Trump. But this is not an edifying account of the positive use of US power – under either occupant of the Oval Office. Trump did not help when he entered the White House in January 2017 The disastrous outcome of the 2003 invasion of Iraq is the main reason for the absence of effective US intervention in Syria. Obama reluctantly authorised the CIA to supply weapons to anti-Assad rebels in Operation Timber Sycamore. But when, after the Ghouta attack, David Cameron lost a parliamentary vote on UK involvement in military action, the news reached Washington “like a bucket of ice water on hot coals”, Warrick writes. Things looked bad enough back in 2013. But Syria’s war, now in its 11th year, has had appalling long-term consequences: 500,000 people have died and half the country’s population has been displaced, either at home or abroad. And Assad remains in power, backed by Iran and Russia. Putin’s proposal to save his ally by persuading him to surrender his chemical weapons worked wonders. In the months that followed, jihadist groups such as the Al-Nusra Front and Isis, which had long insisted that western powers could not be trusted, saw their recruitment swell. Isis started to use chemical weapons that they had captured from the regime. And Assad’s forces continued to use chlorine – in nearly 300 attacks since the Obama-Putin agreement. Still, some parts of this grim story are heartening. Impressive innovation was displayed by US experts who invented the “Margarita Machine” in rural Maryland to water down Syrian nerve agents on board the Cape Ray, the American container ship assigned to neutralise the regime’s sarin, VX and other poisons following the handover of chemical weapons. The author draws helpfully on the memoirs of Ben Rhodes, Obama’s speech-writer, UN ambassador Samantha Power, and Trump’s hawkish national security adviser, John Bolton. But more junior (and often anonymous officials) are franker and more insightful about US policy. Another key diplomat who went on the record is Brett McGurk – now a key figure in Joe Biden’s Middle East team. “We created, perhaps inadvertently, the expectation that the United States was coming, particularly as the revolution militarised,” McGurk said. “Then, with so much money, weapons and tens of thousands of foreign fighters pouring into Syria with little control or accountability, it becomes a total disaster.” September 2015 marked another turning point in Syria’s tragedy. Russia, encouraged by Iran, intervened directly in support of the Damascus regime, gaining permanent access to an airbase south of Latakia. It was Moscow’s first foreign military operation since the Soviet-era invasion of Afghanistan, and a real game-changer. When the US removed itself from negotiations on Syria’s future, Russia became the regional power broker. Trump did not help when he entered the White House in January 2017. During a campaign debate with his Democratic rival Hillary Clinton he signalled readiness to tolerate Assad’s brutality – certainly towards Isis. And once elected, he closed US borders to all Syrian refugees. Senior officials publicly distanced themselves from the by now unconvincing “Assad must go” stance of Obama. Trump then cancelled the CIA’s covert support for Syrian rebels – and of course announced it on Twitter. In Khan Sheikhoun, in Idlib province, in April that year, 89 people were killed by the same sarin nerve agent that had supposedly been destroyed on the Cape Ray. Assad denied involvement, claiming the attack had been staged and that the dead children were actors. The Kremlin backed him to the hilt. Trump’s two subsequent US missile strikes were largely symbolic. The bottom line in this depressing story? Using chemical weapons was Obama’s red line, but “in the end,” as a senior White House official told Warrick, “they (the Russians) were more committed to keeping him (Assad) in power than we were committed to making him go.”