Trump's policy on Syria is being criticized for inconsistency and inadequacy. No doubt. His shifting stance is also far superior to the consistently inadequate (or worse) policies of the oh-so-more-sophisticated EU leadership. Of course the main motive behind the criticisms is hatred of Trump. Yet on what might be thought the most morally significant foreign policy issue, Trump is clearly streets ahead of Obama. Trump bombed Assad. Obama left Syrians to their agonies, calling that decision "courageous", perhaps because he ran the risk of people disliking him.
When Obama let his red line slide, he exhibited an impressive range of moral and political failings. First he welched on the most important commitment of his administration. Then he lacked the courage simply to reverse his stance: instead, he handed the decision to a Congress which he knew would reverse it for him. Then he had the gall to represent his cowardly decision as bravery and sagacity, when in fact it was based on timidity and a parochial ignorance of the Syrian conflict. In other words he not only made disgusting decisions, but preened himself on their alleged excellence.
As for Trump, he acts on impulse. He persistently showed, and still shows, a desire to disengage from Syria. Yet he behaved like a human being. He was appalled by the first chemical attack and when all the terribly moral Europeans confined their reaction to ass-covering, hand-wringing expressions of concern, Trump acted. He felt the need to counter an outrage even though it ran contrary to his larger policy objectives. Then he did it again which, inexplicably, is called a one-off response. (And that without him, the high-minded Europeans would have done nothing: this isn't even open to discussion.) He may be inconsistent, but it is an inconsistency born of decency, leading to a reaction morally superior to the rest of the world's leaders', on a matter of the highest importance.
As for the accusation that his reaction is inadequate, well, of course it is. What would an adequate reaction be? If adequacy means stopping Assad's atrocities, it would require military intervention on a scale that, given the Russian presence, might lead to a major war, with some risk of a nuclear holocaust. Even a slight danger of such an outcome means that an adequate response is out of the question. But to suppose that one or two attacks have no value is wrong-headed. In the first place, the weight of these attacks should not be underestimated: they pose the possibility (now almost the reality) of escalating responses if they don't have their desired effect. In the second place, the attacks establish that violation of norms about chemical warfare against civilians can trigger a military response, even when that response runs counter to the foreign policy objectives of an outraged party. This, arguably, sets a valuable precedent.
In short, Trump showed more decency than Obama, and his very inconsistency makes his reaction all the more worthwhile. He may be the worst president ever in policy terms, but his humanity contrasts vividly with the timid cruelty his idolized predecessor. Bombing Assad doesn't play to his electorate or indulge his prejudices or further his objectives. It transcends those prejudices, sidelines those objectives and honours an obligation to help even Arabs, human beings in distress. That's more than all his cold-fish detractors and their mentors have to show for themselves.
It's not complicated. Either you leave innocents to die in agony, or you don't. Left to its own devices, the rest of the world has shown the firmest, most consistent commitment to the latter course of action. Trump chose the former. That England and France have, as always, done whatever the Americans want them to do hardly redounds to their credit.