Honestly? Myth from my non american researched understanding. The American right has always stayed the same. It's just that the definitions of right wing has become more socially conscious.
I'd wager to say the American right was more hardline even as far as 20 years ago. They supported more extreme versions of the same policies. At one point even before that, the older right wingers in america would say the kind of thing a Jimmy Stewart or John Wayne (both hollywood icons) would say: racist, bigoted things and all they'd call themselves are conservatives and patriots. It just feels like the right has gone more extreme a lot of them support a person like Donald Trump: not the most conservative republican, but certainly the most trashy, uncouth human being to ever hold political office.
But people like Undertaker, does it honestly feel like his policies have changed a lick to become more extreme? no not really. If you ask him, he'd call himself just a patriot and go on a diatribe about how nationalism isn't far right but apolitical, etc. But he's just always has been, and always will be the same amount of right wing. Only now he's also a christian unlike before, I guess.