I'll vote for the republican nominee...
There are legion former republicans decrying trump as not fit for office. In the final republican primary debate, leading candidates once again could not give a straight answer to a simple question: is Trump fit for office? It's the same evasion for the same reason as the notion of "voting for the republican nominee." It's a stubborn refusal to acknowledge Trump's unfitness for office, and wishful thinking that an idealized version of a traditional republican party still exists.
Voters of conscience have a duty to be honest with themselves. To live with intent so their actions align with and reflect their values. If trump defeats the primary field, there will not be a republican nominee. Trump holds no fealty to the party; only fealty to himself. He will not be your retribution. He will be his own retribution. America, like the republican party before her, might not survive it.
Seek Truth. Beware false idols and wolves in sheep's clothing.