The danger to the GOP with this strategy is that it would be likely to solidify the "party elites are the enemy" mindset of many Trump supporters. I could easily see Trump -- who never takes an attack without punching back -- encouraging his supporters to not vote for GOP down-ballot candidates. Many of them would follow suit, and the result would be a Democratic tsunami.
They do not have to do anything very public there. Pro forma references to the presidential candidate could be kept here and there - just not very prominently. Also, spend where it makes sense for the Senate and House - even if it is useless from the presidential race standpoint, while pretty much ignoring the needs of the presidential campaign as such. I doubt Trump has enough of his own machinery or political knowledge in place to monitor where resources should be spent for him and how that would be done. Priebus, probably, can do this in an inoffensive fashion, largely under the radar of the Trump campaign.
