First, retaliation, as I said earlier, is an odd word. Retaliation implies that something was done against the USA.
Then the problem is that this was a unilateral decision. Not even NATO. Certainly not the UN and the problem of using chemical weapons is international law.
Sure that many countries now say they support the strike and were informed, apparently, but it's still a unilateral decision.
Then, the US hardly holds the moral high ground atm. Killing civilians, refusing refugees.
I agree that the UN is highly ineffectual in this respect. It's been a continued problem. Not new at all. But it's not healthy that one country simply takes over.
It's also a(nother) worrying sign about what's to come in terms of world security.
On one hand the US did need to show that they aren't simply going to let other countries loose militarily. Certainly a strong message to North Korea.
On the other hand, and considering how they've been going on in terms of international politics, I worry that they're poking the vipers nest rather than smoking it.
Also, Obama in 2013 asked for Congress approval for action.
They refused.