Party cohesion and the relative strength of the party are key factors. In a two-party system like our's, the Dems should be well-placed, nominally, to resist (if not necessarily stop) the rise of fascism, since the division of the opposition and uniting with useful idiots is often a key tactic in fascist consolidation of power. Italy and Nazi Germany alike.

... but the Democratic party has no cohesion. Neoliberal ghouls try to milk the far-right for all its worth, like Zentrum in Weimar Germany, while the socdems and demsocs in the party actually trying to resist fascism are reduced, by their extreme minority status, to nothing more than admitting that they are defenceless, but not honorless when the hour of reckoning arrives.

For example, in South Korea in the late 80s, while not strictly speaking an expression of fascism (which is generally considered to combine totalitarian revolutionary with reactionary ideas, while South Korea was just a bargain-bin authoritarian military junta), the opposition parties fought the long-lasting authoritarianism of South Korea even without holding a majority. Even in the immensely repressive environment of a police state, they managed to not simply resist the expansion of authority, but reverse it entirely. But it required the diverse opposition groups to present a united front on at least the singular issue of opposition to authoritarian abuses.

And a lot of people taking to the streets. A lot of people taking to the streets.