Let’s think through what would be necessary to halt the use of chemical weapons in Syria.  We know from experience that air strikes do not guarantee it.  Donald Trump loosed 59 cruise missiles against Assad’s regime after sarin, or a variant of it, was used in Khan Shaykhun last spring.  But now it has apparently been used again in Douma.  To stop the attacks, boots on the ground would be necessary to unearth the Government’s chemical stocks, plus anyone else’s, which would mean these taking control of much if not all of the country.  The attempt to build up the Free Syrian Army has not been a success and, even if stronger, it would not have the capacity to act in such a way for the forseeable future.

That would mean western ground troops.  The use of these would be opposed not only by the Syrian Government but by its Iranian and Russian allies.  That could well mean a wider conflict between a United States and its allies, on the one hand, and Russia and Iran, on the other.  Even if did not, Syria could not be ruled indefinitely as an imperial satrapy.  Having gone into it with his troops, Trump would have responsibility for its government.  Parts of the country are in the hands of extreme Islamist groups, such as the al-Qaeda-linked al-Nusra Front, now a member of Hay’at Tahrir al-Sham.  Is it seriously be proposed that such organisations could play a part in governing Syria?  Are they morally better than Assad?  Would giving them political power be in the west’s interests?

If they were to be barred from government in Syria, and this confined to members of the Syrian National Coalition, how would their exclusion be enforced?  Western forces would presumably provide the means.  This would expose the latter to the kind of hit-and-run terror attacks that targeted our armed forces and others in Iraq.  There might or might not be public support for this in France.  There would not be in Britain.  The Iraq experience is too recent and too bitter.  So there would be no strategic logic for such a venture, no democratic support and arguably, given the nature of parts of the Syrian opposition, no clear-cut moral basis for it either.  And all this would apply even were conflict with Russia not to be sparked.  Were this Conservative Government to seek such an adventure, Jeremy Corbyn would oppose it, and Labour suddenly be gifted a heap of political capital.  Tory backbenchers would see this coming and stop it happening.  The Prime Minister’s recent recovery would be undermined and her recent progress reversed.

Neither Donald Trump, for all his unpredictability, will risk such a course, and nor will Theresa May.  Indeed, the President has recently been pushing to withdraw troops from Syria in the wake of the folding of ISIS.  A response to Douma is likely to be confined to missile strikes.  This morning’s reports suggest that there is confusion within the Government even about participation in these.  One report claims that RAF bombers in Cyprus are on standby; another says that May is resisting calls to use them.  The whips will surely be taking soundings from Conservative MPs, and not all these will be as supportive of action as, say, Tom Tugendhat or Johnny Mercer – or, for that matter, Boris Johnson and the Foreign Office.

As James Gray wrote on this site yesterday, the Prime Minister is under no constitutional obligation to consult Parliament before approving participation in a missile strike.  Our judgement is that if she can convince the Commons that Assad was responsible for Douma, and that any strike would be strictly limited, she could take such a course of action and hold Tory backbench support – all without a vote in advance.  This would be more than justified.  But what if chemical weapons are used afterwards again?  Would a cycle of further chemical attacks and further missile responses follow?  What if Assad and his allies are not deterred now, any more than they were last year?  What would Trump and Macron and May do then?