I think this is partially right. There was a fair amount of fascism already baked into the very conservative precepts of the modern Republican Party, such as performative patriotism; the elevation of religion and the military in civilian life; the scapegoating of certain groups of people considered outsiders; corporate control of the national economy in conjunction with the government; and maybe a few others. Cheney, Kinzinger, and Romney at least benefited from all this, if not driving it themselves entirely, and even though they basically left the party, a lot of their fellows who travel along these lines have stuck around.
Then the other elements of fascism really came to the fore in in the past decade—the authoritarian leadership; the desire to suppress dissent; the whitewashing of history; the mass propaganda rallies; the rejection of liberal democracy, pluralism, and individual rights—which I believe drew a new element into the Republican party that had been completely outside of it, where they were considered oddballs and kooks at best, and dangerous actors at worst. They were not already in the party, which they considered part of the liberal order they wanted to topple, but now that the party has embraced the fascism completely, these dangerous elements have found a home within where they now have a veneer of respectability and gravitas they could never have had before.
So I think it's both Trump exposing and highlighting certain noxious aspects of the Republican Party, and the elevation of those aspects and the embrace of other fascist aspects that has attracted extremist outsiders who'd never felt welcome there before.