I really don't understand how someone can think that a 3rd party conservative run will do *long term* damage to the GOP, unless the splinter conservative group remains outside the party beyond 2016 (which it won't, since its only purpose for existing would be to run a non-Trump candidate). It would blow up Trump's chances this time, but why would it matter in 2020 or beyond?
Likewise, I don't see how it's going to hurt downballot, even this year. Most of those voters are going to vote for Republicans for other offices.
Interesting question.
Is 4 years a long enough refreshment period for a failed political stance from a party?