An effective third party would focus first on local, state, and congressional races only in places where they can win. If they can keep the Dems and the GOP from having majorities, the thrid party can hold a lot of bargaining chips while educating the public until they replace the GOP as a major party.
Question: if this is essentially the same plan I've outlined above for conservatives to retake the GOP in two years (the local aspect, especially), then why even bother with the third party? It's an unneeded superfluity.