The GOP is a private organization without a constitutional existence. They can do whatever they want.
Why don’t you believe them?
You are making an important point that is repeatedly missed by many (most?) on this site. Those who talk of "RINO this" and "RINO that" just don't get it. At this point, those who identify as "America first" "conservatives" are the true "Republicans in name only."
The Republican party hates its own constituency. Pure and simple.
To paraphrase Reagan, “I didn’t leave the Republican party, the Republican Party left me.”