Second, it is not at all clear that Trump would make a stronger general-election candidate. Some Republicans say he has more potential than Cruz among white voters without college degrees. Maybe so. But Trump could also do worse among college-educated whites and among nonwhites. What little evidence we have suggests he would be a weaker candidate overall: He’s doing a bit worse than Cruz in head-to-head polling matchups with Hillary Clinton, and much worse in polls that measure whether voters view the candidates favorably or unfavorably.
Some Republicans believe a Trump loss would not hurt their congressional candidates as much as a Cruz loss, because voters will see Trump as his own man while viewing Cruz as a symbol of the party. Dream on. Any nominee will be the de facto leader of the party.
Third, it’s likely that congressional Republicans would find it easier to work with Cruz than Trump in the White House. Cruz’s Senate colleagues think he has been selfish rather than principled when he has picked fights with them. But his self-interest as president would point him toward passing conservative legislation — replacing Obamacare, for example, something that Cruz and congressional Republicans have said mostly the same things about for several years. Trump would be much less predictable.