I don't see how it doesn't make sense to build the justification after attacking. It takes time for people to actually show their disagreement in a way that hurts the state and they're quick to forget once an attack hits them. Also, it still makes sense for the state to build further justifications even if they've already justified it. For this instance in particular, I don't think there really was any justification and if I remember correctly, the population heavily disagrees with this war.

I also think it's a big mistake to equate everything that the state does under Trump to him just being stupid, it makes you blind to what's actually being planned and carried out. You should always try to analyze what the intent behind actions like this is and only if you can't find any reasons at all is it maybe justified to say it's just the government being stupid.