The United States is big. It is "bad" in several meanings. "Big bad" or "big and bad" is often used to mean powerful. There are also lots and lots of ways in which the United States is just bad. I'll leave that open to the interpretation of individuals, particularly individuals from different countries who can sometimes see us better than we can see ourselves.

I don't think there's anything based on context or interpretation here. "Big bad" is just a phrase used to describe something very powerful. The use of this term comes from the "Big Bad Wolf" that appears in many fairy tales, most notably Little Red Riding Hood and The Three Little Pigs. You may think there are bad parts about the United States, but this is not what the sentence is talking about.

Something like this depends largely on the context in which it was said. Or to say it more simply, it depends on when and where it was said.