Donald Trump’s sudden decision to launch 59 Tomahawk missiles at a Syrian airbase is a classic case of doing the right thing for the wrong reasons. In itself it seems a measured retaliation against a barbaric regime that has again resorted to the use of weapons banned by international law.

But “measured” is not a word that sits easily with Trump’s presidential style. The worry, frankly, is that a president who has always been trigger-happy with rhetoric and verbal abuse may now become trigger-happy in a more literal sense.

Firstly, we have to acknowledge that a serious response to the apparent use of nerve gas against civilians by Bashar al-Assad’s regime was a moral and political necessity. Chemical weapons were widely used a century ago, in the first World War, and there was a general sense that this marked a new stage in humanity’s descent into depravity.

Wilfred Owen’s image of a victim in his famous anti-war poem Dulce et Decorum Est haunted the postwar generation: “In all my dreams, before my helpless sight, / He plunges at me, guttering, choking, drowning.”

One of the very few good things that can be said about the horrible 20th century and its orgies of mass murder is that some kind of line was drawn. Even the Nazis did not use chemical weapons on the battlefield.

Irrational

Perhaps this horror is irrational. Is it more barbaric to incinerate a child with a conventional bomb than to poison her with gas? But we have to hold on to whatever moral boundaries we have managed to salvage from modern history, and this is one of them. The sight of people “guttering, choking, drowning” from the effects of poison gases still haunts us in a peculiar way.

The Assad regime’s mass use of nerve gases against civilians in the early stages of the Syrian civil war provoked an outcry that in turn led to the supposed destruction of its stocks of chemical weapons. If it could get away with such a flagrant demonstration that it had made fools of the international community the taboo would be broken, perhaps for good.

In principle, of course, the response should have come from the United Nations, but we know that a UN in which Assad’s ally Vladimir Putin has the power of veto would not even condemn the attacks near Idlib on Tuesday, let alone punish them.

Chemical attack: a Syrian child is treatmed after Bashar al-Assad’s regime apparently used nerve gas on civilians. Photograph: EPA

Trump did the right thing, then, but there are four main reasons to be concerned about his reasons. First, there is the chaotic policymaking. In 2013, when Assad first used chemical weapons, Trump tweeted: “President Obama, do not attack Syria. There is no upside and tremendous downside. Save your ‘powder’ for another (and more important) day!”

In the presidential-election campaign Trump attacked Hillary Clinton’s aggressive stance on Assad: “Now she wants to start a shooting war in Syria in conflict with nuclear-armed Russia. Frankly, it could lead to World War III and she has no sense.”

Just last week Trump was signalling that the US had no interest in removing Assad from power and that its sole concern in Syria was the defeat of so-called Islamic State. So there is no evidence that the Tomahawk attacks in the early hours of Friday morning are part of any thought-through strategy or moral position.

Secondly, what there is evidence for is that the attacks are merely the most dramatic examples of Trump’s habit of governing by impulsive responses to what he sees on television. His highly emotional speech announcing the attacks, in which he spoke of Assad killing “even beautiful babies”, was typical of the way he reacts to everything else he sees on TV: with hyperbole or horror.

Gut reactions

On Wednesday he told White House reporters of his visceral response to the images he was seeing from Syria: “I will tell you that attack on children yesterday had a big impact on me – big impact. That was a horrible, horrible thing. And I’ve been watching it and seeing it, and it doesn’t get any worse than that.”

We should, of course, respond viscerally to such horrors, but people in power should not be driven by instant gut reactions to media images. The retaliatory strikes look like an escalation of Trump’s narcissistic belief that the world should be shaped according to his personal moods.

Thirdly, the rational calculation behind these strikes, to the degree that there is one, is unlikely to have much to do with moral boundaries or long-term geopolitical consequences. Trump doesn’t have moral boundaries, and the strikes contradict what he had set out as his long-term Syrian strategy.

The political calculation is much closer to home and much more cynical. Trump’s biggest problem – the one that already threatens to derail his presidency – is the close connection between his campaign and Russian officials. The investigations by the intelligence committees of both houses of the United States Congress are beginning. What better way to distract from them than to attack Putin’s ally Assad?

Lastly, the fear must be that, having got a taste of military action, Trump will become addicted. For an adrenaline junkie, whose political style demands constant conflict and whose short attention span demands quick “fixes”, the immediate high of destroying an airbase must be euphoric. As pesky domestic realities bog him down, the lure of that high will be increasingly irresistible.