I remember having several times heard of far-leftist populists who finished far-rightist populists, the only example i've in my mind is Mussolini but I remember having heard of it for several others.
Though, I can't remind having already heard about some far-rightist who finished far-leftist.
Has it existed?
From Far-left to Far-right: Jacques Doriot and the Alsace Communists during WWII come to mind. There are quite a few actually... Wasn't Oswald Mosley once a Labour MP?
From Far-Right to Far-Left: That's much harder. At least among major figures (obviously on lower levels alot of that went on, if they could get away with it, in Eastern Europe c1942-1947).
