The three pillars of the Republican party were conservatism, religion, and race. I'm not saying every R is concerned about all 3 of these, but that they couldn't win elections without all 3 of them. Over the past 50 years, traditional conservatism has been hard pressed to explain itself to the working class in light of the rising prosperity of liberal democracies, and has become further detached from reality. People are becoming less religious, and more racially diverse. I think the R's realized that they were running out of runway, and also figured out how to exploit nearly 100% dominance over the "new" media.