Like it or not, the US was founded by Europeans, for Europeans (check the early immigration laws) on political ideals that were born in Europe and are generally balked at in other parts of the world. In the multicultural hell that is the modern US, the GOP is implicitly the political party of whites, since they still have an interest in preserving these ideals such as gun rights, freedom, limited government, etc.
If America becomes majority non-white, these ideals will not survive, and multiculturalism will always ensure that acting in racial interest will outweigh any amount of "muh education on economics and American ideals."
It's a difficult pill to swallow, but it's the reality. This is why communist leaning politicians want a greater non-white population, and if you're a thinking person, the blatant anti-white racism in the mainstream should activate your almonds.