In the case of Hitler and Mussolini it wasn't some organic process of arriving at different solutions to similar problems. They literally looked at how the early socialist movement was successful with working people and outright copied the language and symbolism and then modified it. They were very explicit about what they were doing, hence the "socialist" label in the Nazi name despite having no socialist program. They wanted to recruit those people and divert them to their cause.

Every time I hear one of these Trumpite nutbars go on about the "mainstream media" I have to give my head a shake, because the phraseology is the same as what you'd overhear at a Food Not Bombs event in the 90s or something. But the intent and the ends are entirely entirely different.

They've taken the vacuum left by the disintegration of the left, and filled it nice and full of some really awful stuff.