Secret? You can say a lot about the USA in Venezuela but secret isn't it and of course it was authorized congress explicitly granted the president the powers to do it.
Why do people go out of their way to criticize Trump like this?
Attacking other countries without declaring war is a staple of pretty much every US president since WW2, republican or democrat. Carter is the only one who stands out (ironically, despite the fact that he had a good cause to invade Iran).