The USA is already a functional oligarchy. (Or, more accurately, a plutarchy.) It has been functioning as such for some time — since 1992 at the latest, although the roots of this system go back to before the Declaration of Independence — it's a recurrent failure mode. Historically such periods last for a few years then go into reverse. However, this time the trend has been running since 1980 or even earlier. What we're now seeing are the effects of mismanagement by the second generation of oligarchs in power; the self-entitled who were born to it and assume it to be the natural order of things.