‘The only reason I’m supporting [Mitt] Romney is because he can win the election,” an Iowan named Tim McCleary told the Washington Post in late December. It seems to be a common sentiment among Romney supporters. But Romney’s critics are putting forth a vigorous set of counterarguments that can’t be easily dismissed.

Some say that he is actually a weak candidate: someone to whom voters have never really warmed. Or they say that if nominated he will not be able to motivate conservatives to show up to vote for him. Some conservatives say that electability is overrated: Merely electing someone who …