A Syrian doctor treats a boy following a suspected chemical attack in the town of Khan Sheikhoun. Credit:AP We've been here before. In 2013 a poison gas attack that killed an estimated 1400 and wounded thousands more in the Damascus suburbs was the crossing of a "red line" that former President Barack Obama had warned would trigger a military response. But Obama didn't bomb Assad's bunker. Instead Moscow, Washington and Damascus struck a deal under which Assad would surrender his chemical weapons arsenal to the international community.

A victim of a suspected chemical attack receives treatment at a makeshift hospital. Credit:AP But with Tuesday's horrific attack being one in a series since that deal was signed, it's clear that Assad held back some of his poisonous stocks. In 2013 Trump in particular and Republicans generally mocked Obama. A child victim of the chemical attack is treated at a makeshift hospital. Credit:AP But now Trump is President and the GOP rules Washington and the whole Syria mess is infinitely more complicated.

They own it, so what will they do about it? What can Trump do in the face of such a wilful demonstration by Assad of the seeming powerlessness of the world to deal with him? The attack coincided with a conference of European governments in Brussels, which pledged billions of dollars to rebuild Syria after the war so that the refugee masses in Europe might return home. While the White House was blaming Obama's inaction for Tuesday's attack, the State Department was blaming Assad and his Moscow and Tehran sponsors, with a spokesman urging the Russians and the Iranians to rein in Assad. White House spokesman Sean Spicer described the gas attack as a "reprehensible" act against innocent people "that cannot be ignored by the civilised world."

But in keeping with the administration's singular focus on countering IS, he insisted that the US was unlikely to change its thinking on Assad because of Syrian "political realities". "There is not a fundamental option of regime change as there has been in the past," Spicer said at his daily press briefing session. "Somebody would be rather silly not acknowledging the political realities that exist in Syria. "What we need to do is to fundamentally do what we can to empower the people of Syria to find a different way." Spicer refused to discuss actions Washington might take.

Then he went for Obama: "These heinous actions by the Bashar al-Assad regime are a consequence of the last administration's weakness and irresolution." As much as Obama loathed Assad, he worried that there would be a vacuum in the absence of the Syrian leader, which would be filled by the likes of IS, al-Qaeda and other extremist groups. Despite expressions of horror at the White House over this latest gas attack, Trump has not been unduly bothered by the carnage of a six-year civil war in which more than 400,000 are estimated to have died. Last year Syrian diplomats speculated that they would come under less pressure from Trump than from his rival Hillary Clinton if she was to win the November election. And sure enough, as reported this week by The Washington Post, when Blackwater founder Erik Prince had a secret parley with a close associate of Putin's in the Seychelles in January, an agenda item as they explored a Washington-Moscow back channel was a deal to resolve the Syria crisis.

Trump too has alluded to some kind of joint effort with Moscow in Syria. But that now becomes an even more complex proposition. Because Moscow has come to depend on Syria for a foothold in the Middle East, and in getting into bed with Vladimir Putin, Trump also would be cozying up with a trio that, in the eyes of most in Washington, is utterly unsavory – Assad, Tehran and the Lebanon-based Shiia militia, Hezbollah. Both Haley and Tillerson earned a ticking off from Republican senators John McCain and Lindsey Graham on their seeming indifference to the plight of ordinary Syrians. Warning against any "Faustian bargain" with Moscow, McCain used blunt language: "Syrians can't decide their fate as they're being slaughtered."

"Trying to fight [IS] while pretending that we can ignore the Syrian civil war that was its genesis, and fuels it to this day, is a recipe for more war, more terror, more refugees, and more instability. "I hope President Trump will make clear that America will not follow this self-destructive and self-defeating path." And in a statement after Tuesday's gas attack McCain seemed to dare Trump to not act against Assad: "Assad believes he can commit war crimes with impunity and [the question is] whether we will take any action to disabuse him of this murderous notion." Loading Accusing Trump of "the biggest mistake" since Obama had failed his own red-line test, he said: "I hope these reports are not accurate, but if they are the war in Syria will never really end as the Syrian people want Assad removed from power".

But in a sense, Haley and Tillerson were firming up what had been Obama's de facto policy – general inaction for fear of making an appalling civil war more appalling.