I don’t think RP and the RNC have the authority to decide on candidates for House of Representatives, Senate, Governor, or whatever. Local voters can decide what they think about any candidates who are willing to meet state/local filing requirements.
They can decide whether to provide RNC backing and support...
The RNC can decline to endorse them however and that affects finances. I always note who the Wake county NC GOP endorses although it does not decide my vote.
They are a private organization, and as such can determine who may or may not be a member entitled to the use of the name, trademarks, logos, and copy writes.
RNC can dry up the money for them!!!!