The base of the republican party has always been conservatives. Conservatives are by definition people who seek to 'conserve' the status quo. They are people who don't like change, and don't want it. Mostly because they are also the people in society who are benefitting most from the 'way things are now'. That it, the very wealthy, the wealthy, and the well off upper middle classes. also some working class folks who have good benefits and job security, and who are particularly given to obedience to authority.
These are not the people we are currently discussing as the republican "base": radical religious conservatives that want America to become some fantasy version of "bibleland", and political extremists fueled by racist, religious, and sexual bigotry, fear-mongering and a general anger that they are no longer the white male power class that they once were. These people aren't even conservatives, though they seem to have cooped the label. They are radicals, and extremists. They are a lunatic fringe that the republican party has been pandering to, to gain their votes because the party can't win elections, otherwise. Their real base is just not strong enough on it's own because of the massive and growing income disparity in this country. But this deal they made with the 'devil' is coming back to bite them in the rear end, because the extremists are now all 'fired up' and taking over their party, and they are chasing the real republican base away.