One of the reasons to be skeptical that Rick Santorum could win the Republican nomination is that we now have a pretty good idea of how the vote will play out from state to state — and the coalition that he is building seems short of a majority. It is not that Mr. Santorum’s delegate deficit is mathematically insurmountable. But he’s behind, and he is very unlikely to win states like New Jersey and California that either have a lot of delegates or use winner-take-all rules to award them. That might not leave enough fertile opportunities for him to gain...