Originally Posted by teh603
He's probably been excommunicated from the party. They can do that in a lot of states, especially ones where you have to be a registered party member to vote in the primary.
They can try it in New York, but it's extremely rare, and liable to be overturned if you go the expense of a court challenge.
Googling, I can't find a modern example of anyone having their major party registration revoked. If the GOP had tried to do this, it would be all over the internet.