There is generally no legal requirement that a political party use democratic or otherwise ‘fair’ methods at all to choose a candidate.
Any ‘adjudication’ of this would seem to take place within the Republican Party.
Fine. Then Carson needs to take it to the correct organization who handles this cheating - if it’s only the Republican Party, so be it. If they reject his claim, we need to broadcast loud and clear that the Republican Party is corrupt (which it is, anyway.) And we need to broadcast loud and clear that Cruz is a cheat.