I always hear that the Republicans used to be like modern Democrats if you go back far enough. That things started on this current path about 30 years ago.
From my understanding the parties used to be geographical rather than ideological, or at least much more than they are now, before the Civil Rights act. That put the country on the path to polarisation.
The thing with the tea party too, is that they come from bleach white districts, districts not affected by national demographic changes, districts that still live in the sixties. They think they're winning this battle because they are... In their districts, comprehensively. People talk about the conservative bubble but these literally are bubbles.