IN the aftermath of the missile strikes in Syria on Friday, the US president delivered a typically Trumpian message via his favourite medium. “Mission accomplished!” he said on Twitter, possibly unaware – or not caring – that George W Bush used the same phrase six weeks after the launch of the US-led invasion of Iraq in 2003 - and we all know what happened there.

In the months and years that followed the intervention in Iraq, the words “mission accomplished” came to represent the arrogance of a mission that was anything but. And it is extraordinary that in an international situation that is currently so delicately balanced and dangerous, Donald Trump should have used the phrase again.

The use of “mission accomplished” also suggests we know what the mission in Syria is, but do we really? Theresa May did not go to parliament to explain the exact nature of our aims in advance of the strikes – and, more importantly, she did not seek parliament’s approval, although she will try to do so retrospectively today. Prime Ministers do need to have the right to act swiftly in the national interest when required to do so and sometimes to do it without a Commons vote – and several PMs have exercised that right in the past. But the civil war that has been raging in Syria for seven years does not come anywhere near passing that test.

The Government’s excuse for not going to parliament before the strikes was particularly unconvincing. Mrs May said she had to consider, with Britain’s international partners, what action was necessary and then do it in a timely fashion. But why not recall the Commons last week in time for a debate or a vote?

Alternatively, the Prime Minister could have delayed British action until the Commons had had its say - after all, the situation in Syria has been shockingly clear for years and it is hard to see how a delay of a few days could have made it much worse. The fact that the Prime Minister did not sanction a delay suggests that the pace was being set not by Britain but by an impulsive, twitter-happy President and that the Prime Minister was unwilling to go against him.

What makes the situation worse is that the case for military strikes that Mrs May could have put to parliament is one that had every chance of standing up to the rigours of a Commons debate. Democratic governments have a responsibility to uphold international law and human rights, but there is clearly also a British national interest at work here.

As we know, chemical weapons have been used by the Russian-backed regime in Syria, but they have also been used recently on the streets of Britain. In supporting air strikes, Mrs May could have made the case to parliament that she and our allies were sending a message to Russia and the world that no one can use chemical weapons without reprisal - in Syria, Britain or anywhere else.

Of course, it seems likely that Mrs May avoided putting such arguments to parliament before the air strikes because she calculated that she would have lost the vote, as David Cameron did when he tried to get parliamentary approval for military action in Syria in 2013.

However, the risk of losing a debate cannot be an excuse for not having it. As Prime Minister, Theresa May is facing the troubling test that so many PMs eventually face and has ordered the British armed services into action, but in doing so she has failed another crucial test of democracy and leadership.

It may be that the strikes the PM has sanctioned will act as a deterrent without making the situation worse. But whatever happens, the PM should have done what she had every opportunity to do and sought the approval of parliament for a risky military action that could have serious consequences for us all.