Review the French Revolution.
The Leftists of the time (when political terms “left” and “right” were actually coined) operated by continuous purges: extremists would eliminate (often violently & terminally) moderates for not being Left enough; these extremists would then (having eliminated the moderates, simple statistics) become the new moderates, which would then be likewise slaughtered by new and even more extreme extremists. Lacking any concept of forgiveness (which moderates religious fervor), this continued cycling until “equality, fraternity, tolerance” only applied to anyone absolutely in line with Robespierre - who was himself thrown out a window.
By absolutely abandoning the definition of “Nazi” and only retaining the designated awfulness imputed on whomever the term is applied to, modern Leftists are beginning a similar cycle. Those who were “extreme” not long ago - Hillary, Obama, Pelosi, etc - are now increasingly dismissed by neo-Leftists like AOC, Bernie, Buttegeig, etc ... who are unwittingly already in the crosshairs of the next wave of even more extreme Leftists (see Project Veritas’ undercover of the Sanders campaign). Media being widespread and persuasive, we fortunately have not seen much terminal violence in these cycles, but nobody will be surprised when it starts.
History doesn’t repeat, but it rhymes ... and this “Nazi!” refrain sounds awful familiar.