For concrete data, take a look at for example the Netherlands; where right-wing extremist parties led by Wilders and Baudet have shifted public opinion such that the 'moderate right-wing' parties have taken on considerably more xenophobic and fascist rhetoric over the past few years, because that was the only way for them to compete against Wilders' and Baudet's brand of populism.
This is fundamentally the problem with fascism; it doesn't come into power through people saying "I'm a fascist". It comes into power by 'infecting' everything around it, and gradually shifting the Overton window such that the populace will eventually willingly grant power to the fascists.
That also means that such a 'fascist takeover' can only be detected and interpreted through a trend in public discourse, not as an easily calculable single metric.
This is fundamentally the problem with fascism; it doesn't come into power through people saying "I'm a fascist". It comes into power by 'infecting' everything around it, and gradually shifting the Overton window such that the populace will eventually willingly grant power to the fascists.
That also means that such a 'fascist takeover' can only be detected and interpreted through a trend in public discourse, not as an easily calculable single metric.