I don’t think it’s Trump in particular as an individual that Republicans are frightened of, but the cleft stick of their own making that they’re caught in, whose formation pre-dates Trump. The Trump-supporter “personality cultists” are deeply uninformed and misinformed, which is not unprecedented in American politics, and also unified by instantaneous communication and dissemination of their misinformation, which AFAIK is unprecedented in American politics.
IMO the not-entirely-deliberate project of creating such a fanatically partisan, low-information and high-distrust volatile base of conservative voters goes back at least to the days of the “Moral Majority” movement in the 1980s. It was nurtured by the growth of Fox News, talk radio and other heavily right-wing media outlets, the jingoism of post-9/11 and the Afghanistan and Iraq wars, theocracy-lite cabals of evangelical/fundamentalist conservative politicians at all levels of government, and subsequently the Tea Party reaction to the election of Obama. Its anti-liberalism, xenophobic ressentiment, anti-government and anti-expertise disdain, and credulous ignorance have culminated (hopefully but by no means certainly) in Trumpism.
Throughout, the project has largely been bankrolled by fossil-fuel companies that have had a great deal to lose from any kind of environmental regulation, especially of the sort that would be required to seriously combat climate change, and a lot to gain from Middle East wars and an oligarchic political structure.
So in a sense we’ve had a sort of perfect storm of contributing factors, ranging from reactionary backlash against the social reforms of the '60s and '70s, to neoliberal high-tech corporate globalism (for which Democrats are just as responsible as Republicans, AFAICT) that has undercut the working and middle classes, to a major global environmental crisis that oligarchs can’t afford to acknowledge honestly, to drug abuse epidemics, “culture wars” controversies on guns, abortion, education, etc., terrorism, war, and now global pandemic.
It’s not so much that Republicans are afraid of Trump qua Trump: it’s just that Trumpism seems to be the only way their base can be reached. In the eyes of a significant, and critical, portion of their voters, any Republican who opposes Trump is just as bad as a liberal. There’s no point trying to appeal to those voters with facts or logic or practical common sense or critical thinking, because they’ve been sedulously encouraged by decades of conservative propaganda not to value those things.