I don't even know if the Republican party can or will be changed. I read a
good article from Reason that argues he is a result of a party in apocalypse more than anything. And to some degree I agree that his rise is a result of a party and a people that are not healthy politically (distrust in all major institutions, constant anger, low optimism, etc.). This may literally be the destruction of the Republican Party, however I doubt a whole new party will be formed, so here's how I imagine it would be transformed if Trump wins:
The Republican party becomes far more nationalistic - and yes, a little more fascistic and authoritarian. On the economic front, free markets are not a priority, instead the government should do what is deemed 'right for America'. So tariffs on other countries goods and subsidies for certain producers or products (we have that right now, the difference will be that these will sold as populist and anti-cronyist, to help the common people) if it brings back jobs. The talk becomes all about jobs, and American jobs specifically (again, more nationalistic). Now, I still expect the party to remain on its traditional taxation and regulatory rhetoric, so it won't be like this huge transformation. On immigration, the regular policies sold will be that people need to be deported before they come back, immigration overall needs to be cut down, and that there needs to be a lot of security at the border. On foreign policy, there will be a demand for quick and easy wars if any, but no nation building and no intervention otherwise (very different from the standard Republican position now). However, it will be the same party in the sense that when they feel security is needed, civil liberties come far behind or go out the window.
But more than anything else, Trump's ideology can be summed up as "trust me, I know how these things work, I know how to get it done and we will be successful", a simplistic, non-substantive, and deeply authoritarian sentiment that worries me a lot.
