The Republican party became a sellout, he should create his own Populist party to replace them.
Theodore Roosevelt use to be a Republican, but he created his own party called the Bull Moose party while in office and a majority of his supporters joined it.
More realistically, he will ask for and receive resignation from more than half the GOP members, and hopefully these vacancies are replaced by Trumpians. At that point, he can pretty much declare his own party
a party within a party, like the tea party? it should be called the patriot party and there should be lions and eagles