I don't think there's much of a choice from their point of view. If they end-run Trump they're either going to have to get Cruz to buy in by giving him the candidacy or lose his voters too. And Cruz hasn't committed to any such games. Foisting Ryan or Romney, or God help us, Bush, on us and alienating both leading candidates' voters is a recipe for a debacle that will end the party.
I think they’re more interested in rubio’s voters.