Fascism is well defined, it is capitalism in decay, it is a desperate lashing out of the parasite class when they become incapable of forestalling the TRPF. Fascism is simply capitalism with the mask off. It is only "not a very well defined term" within the capitalist superstructure because they don't want people oppose capitalism, so the definition deliberately muddied. There are many things that are not poorly understood, but must be made to be poorly understood.

Would be more accurate to say capitalists I suppose, who inevitably give way to fascism.

The US is a bourgeois/capitalist dictatorship built on the genocide of millions of native Americans. I think most socialists would say it's not quite a fascist regime just yet, but it has a history of supporting such regimes and is currently supporting a fascist colony committing a genocide in Palestine.