It started long ago.
Absolutely.
What I’m getting at is that today, they are so convinced of it that they run radical leftists for the top job and cave on so many core issues that they think nothing of doing it. 30 years ago, the farthest left Rockefeller Repub was far outside the mainstream/conservative side of the country/party. Sure there were a bunch, but look at the issues they pushed. Rabid conservatives by the standard of the Bhhner/McCain/Romney wing of today.
No GOP would or did so casually propose moderating on abortion and gay anything was shoved far into the closet.
But you are totally correct. the left swing did not start anytime recent. It just went into overdrive ‘mainstream’ fullmetal Democrat recently.