Either a 3rd party or more and more previous Republican voters just stop voting in presidential elections. Boner seems ready to add more evidence for those who believe there is actually little difference between the two parties on the major issues of national sovereignty and globalism.
Right after an election is the time to start. You can raise funds. You can vet candidates. No idiots like the pubbies put up. Start collecting signatures to get on ballots. Maybe a half dozen states to start and let it grow from there.
There will be push back from the established parties who don’t want the competition. I have no illusions as to how fast a process this would be but a few congressional seats could certainly be a reasonable target with a 2 year lead time.