If the leading candidate was to drop out of the campaign after most primaries or even during the convention, individual delegates would likely decide the party’s nominee on the convention floor. That would shine a spotlight on the normally niche question of who those actual delegates are. There would be a messy political battle in every state over who would get to be a delegate (if the vacancy happened before many of those people were chosen) and then who they would ultimately support. Even people who did not run primary campaigns could ultimately be considered. You can assume, for instance,...