An important article by Max Boot, an already fairly moderate conservative, writing about his departure from the Republican party. points out that movement conservativism has engaged in driving to the right and pushing out the moderates. Again, and again. In 1996, Barry Goldwater and Bob Dole described themselves as “liberal” compared to the GOP at that time. Now, former rank-and-file conservatives are leaving the party as it pushes forward into a neo-fascist direction.
I also recommend listening to the August 9, 2018 episode of Stay Tuned (with Preet) where the former SNY-DA talks with GOP Strategist Steve Schmidt. In it, Steve narrates what went wrong with the GOP from Palin to Trump, and how the party has embraced a dark side.