Unfortunately, that won't scare him at all. All of the sitting senators know that the party leadership will defend them when it comes to the primaries.
They also know that once they win the primary, that you will hold your nose and vote for them anyway.
The only thing that will get their attention is if you tell them that you will vote 3rd party in the general election if he is the GOP nominee.
I have said I would vote third party in my [numerous] emails. I should probably have said it on the phone, but it was a very intense moment and I wasn’t thinking with crystal clarity.