As a practical matter, defeating RINOs in primaries is a lot easier than starting a 3rd party.
Suppose there is a district that is 60% Republican and 40% Democrat. If you get 51% of the vote in the Republican primary, your candidate wins. (assuming the RINO you beat in the primary doesn't throw a tantrum and run as an independent and split the Republican vote)
Suppose you run as a 3rd party candidate, with 51% support from Republicans and 0% support from democrats. In the general election, the Democrat then wins with 40% of the vote. (with the vote being 40%/30.1%/29.9%)
If you start a 3rd party, you're just throwing elections to Democrats.
As a practical matter, defeating RINOs in primaries is a lot easier than starting a 3rd party.
Suppose there is a district that is 60% Republican and 40% Democrat. If you get 51% of the vote in the Republican primary, your candidate wins. (assuming the RINO you beat in the primary doesn't throw a tantrum and run as an independent and split the Republican vote)
Suppose you run as a 3rd party candidate, with 51% support from Republicans and 0% support from democrats. In the general election, the Democrat then wins with 40% of the vote. (with the vote being 40%/30.1%/29.9%)
If you start a 3rd party, you're just throwing elections to Democrats.