Why not both? We are absolutely an empire in decline. And we just elected someone who spoke about the "enemy from within" and made numerous threats of turning the military on the American people.
It's not been a hugely impactful country in the way that the roman empire was, so at the very least it's not the latter. I know people like to say "pax americana" was a thing, but let's be real - even when the US was actually doing well it wasn't a force for peace and development.