"Justified" in what sense? Who does this administration - or indeed USA in general - answer to?

Folks there's nothing new or insane here. Countries attacked other countries all throughout human history. The surprise is when they don't.

Now it's not super hard to understand why Trump is fixated on Venezuela in terms of geopolitics. There's a decision by this admin to bolster US in the western hemisphere, possibly in preparation to coming to terms with a bipolar world split between US and China. So the US is now meddling with Canada and Greenland. Now with the shift towards the right in Latam (Milei in Argentina, Bukele in El Salvador, Kast in Chile) Trump is just pushing a few more bricks to create a more uniform American-led sphere. Plus, Venezuela was very close with the Iranians and Russians, so removing this regime surely serves some strategic goals.