Party changes in terms of what each party represents and their platform happen all the time. It's why we don't have Federalists and Democratic Republicans, it's why we people so often look at the name "Democrat" in the 1860's and seem them as the party that voted against 13th amendment and all of that, not realizing that both parties had "conservative" and "liberal" right-left elements within them both.
All we're witnessing is what happens when a party has co-opted a losing strategy and losing outlook. We're no longer becoming this majority nation of white, Christian, heterosexual only, male dominated society, and all of this turmoil from the Republicans, and the infectious Tea Party people is basically the realization of that coming. Those who are in power, or perceive they are in power don't leave it quietly. It's basically the death throws of it. Sure, we got a long way to go before any of that is normalized, but it is clearly the trend.
If the Republicans didn't double down on trying to exclude everyone (and Democrats therefore have been more than happy to let basically anyone in, which will hurt them once the Republican recalibrate) they could get plenty of conservative gay men to their banner, or if they didn't hate immigrants/Mexicans, their more conservative outlook would actually be more appealing to rather conservative views of Catholic Hispanics and Muslims, but right now, they aren't welcome. And if they didn't have so many open racists they could get way more of the African American vote. But since they didn't do that and instead go and against all these groups, the lose, and have lost over time, increasingly larger amounts of voters.
It wasn't that long ago you didn't have to even worry about those groups, they were small and politically marginalized both all parties. It wasn't that long ago that this concept of a "real" American even came into being. It's rather recent, like Nixon recent with the "silent majority" that this idea of a "real" America even was a thought. And back in the 60's, that ideal did match reality, well that reality doesn't match that ideal anymore.
Once the republicans shed the dead weight around their neck, get more in touch with what actually makes them conservative, and can stop trying to exclude everyone, they will pull people way from the Democrats, and they will undergo a similar transformation if/when the Republicans start winning against. Both are inevitable, both have to happen as time goes on, and unless we radically change our political system, two parties is all that this country will have. Sit back and enjoy the song and dance.