Hyper presidentialist state that allows one administration (and realistically one person) to start a war against another nation without having authorization from congress.
Actually, I'm in favor parliamentary republic with proportional representation, but words have meanings, and "authoritarian" is impossible to apply to a country with electorally changeable power by definition. Or a one with working separation of powers. And plenty of other attributes present in the US.
This happened a few weeks ago, actually.