It may be that Donald Trump’s missile strikes against one of the Syrian regime’s airfields achieve their purpose – namely, deterring any further use by it of chemical weapons against innocents.  If so, he will have drawn a red line over the use of chemical weapons by rogue states; prevented their future use in Syria while avoiding being further drawn in to the conflict, and succeeded where Barack Obama failed.  The President will have demonstrated nerve, decisiveness and good judgement – in contrast to his predecessor, who has been so over-puffed in BBC-land Britain, and thus (inevitably) over-rated.

But it may be instead that the Assad regime, backed by Russia and Iran, deploys chemical weapons again.  What then?  Trump would have a choice: to order further missile strikes (or some other form of military action), or to back off.  The latter course would risk an impression of weakness.  The former would be to raise the stakes.  At which point, the question would arise of whether it is in America’s strategic interest, or that of its allies, to be drawn into Syria’s civil war on one side in the same way that Russia has committed itself on the other.

There is no solid basis for such engagement.  This is a horrible civil war with no heroes – reminsicent in its ferocity, contempt for human life, flagrant propaganda and involvement of outside powers of the Spanish civil war.  We view with contempt the conspiracy theory view, pushed on blogs and Twitter by the Putinbots, that this week’s attack on Khan Sheikhoun, which left the best part of 100 people dead after the apparent use of Sarin, was a false flag operation.  None the less, the various ISIS and Al Qaeda-flavoured groups that make up much of the other side of the war have tried to get their hands on some and may have done so already elsewhere.  They have no less contempt for human life than Assad, and pose a more immediate threat to our security: 7/7, the murder of Lee Rigby, the recent Westminster car-and-knife attack and the mass of plots that the security services and police have disrupted over the last decade or so have been planned and executed by Sunni-aligned extremists, not Shia ones.

All this casts a searching light on Trump’s decision to order these missile strikes.  During his campaign for the Presidency, he made it very clear that ISIS would be Enemy Number One of a Trump administration.  Now he has turned on the Syrian regime.  It would be simplistic to argue that what is bad for Assad is good for ISIS: as we have said before, the former has spent much of the war deliberately targeting non-Islamist and other Islamist groups, with the cynical aim of seeking to force America to choose between him and ISIS.  None the less, the missile strikes suggest strategic confusion.  First, the Trump administration signalled that it would no longer seek Assad’s removal.  This – arguably – led to the regime concluding that it could now use chemical weapons safely.  Now it is reported that the President seeks Assad’s removal.  Has Trump’s decision shown human decency? (Some 30 children died at Khan Sheikhoun, vilely murdered by chemical weapons.)  Or has he demonstrated dangerously erratic judgement?  The Islamist groups may not have used chemical weapons, but they have committed atrocities every bit as sickening.  How should those be weighed in the moral balance?

It is ironic that Trump – who was better disposed to Russia during that presidential campaign than any previous post-war Republican candidate; who has seen it accused of improper relations with the Putin Government, and has lost a national security adviser over the issue – is now closer to a stand-off with Russia, the Assad regime’s patron, than his predecessor.  Some of the President’s most prominent critics within his party, such as John McCain and Lindsey Graham, have rallied to him.  By contrast, many of the isolationists who helped elect him will be downcast.

Theresa May needs Trump for help with the Brexit settlement.  A free trade deal with America that worked for Britain would be icing on the cake.  But she will remember the backbench revolt over proposed missile strikes against the Syrian regime in 2013 which left David Cameron’s foreign policy rudderless.  Downing Street will not want to do anything that might risk a repetition.  Her instinct will be to act as a force for restraint.  It will be reinforced by the knowledge she acquired as the longest-serving Home Secretary since the war of the security threats to Britain.  As if the long-term challenge of Brexit were not enough, she now faces a short-term one of the first order.