Another person who doesn't understand the first amendment. The first amendment says that the government can't mess with your free expression. They can't put you in jail because you say something they don't like, they can't shut down a news paper for reporting on things they don't want, and so on. It does NOT say that people have to listen to whatever you say, like it, and not respond in any way.
This guy didn't have his rights violated at all: He said something extremely stupid, and people then used their first amendment rights to express that he's a jackass. His political party decided that because he'd pissed off lots of voters, they weren't interested in supporting them. They aren't required to support anyone, the choose the candidates they like. He realized he'd fucked up, and had no chance of wining, and so withdrew.
Nothing improper here. You seem to think that the first amendment should mean speech without consequence. Of course that doesn't work without infringing on the rights of others. If you say something I don't like, I have to be free to say I don't like you for it, or my freedom of speech is being infringed upon. I have to be free to refuse to talk to you, do business with you, etc or my freedom of association is being infringed upon.