How has the Republican party gone from the party of Lincoln to the party of Trump?
It is like going from the diamond on the hill to a giant turd in the toilet.
Conservative voters haven't changed much in their values in the 25+ years that I've been observing US politics. The only noteable movement is that they've become less uniformly opposed to gay marriage, more consistently in favor of freedom of speech, less hawkish on foreign policy, and more protectionist on trade and immigration. Other than the fact that the mainstream left flipped on their immigration views when they decided that favoring the American working class was oppressive to foreign workers who want to live here, all of the movement that the critical mass of right wing voters have made in my lifetime amounts to a slight slide TO THE LEFT.
The fact that you think that the republicans have gone radical is due not to the right wing going extreme, but rather is likely due to the fact that you have failed to notice that the people from whom you get your political information have descended into ideological fanaticism. They were pretty subtle about it. Fifteen years ago they would make fun of paranoid right wingers when we'd point out that their repeated framing of the US as the villain in every world conflict and throughout history seemed to imply a hatred for the country itself. Now, as the left is calling us racists for not wanting to tear down all of Americana, you're acting like we're the ones who have changed. Yeah, no, try again.