At the moment Rick Santorum appears to be overtaking Newt Gingrich as the principal challenger to Mitt Romney. Santorum has won more contests than Gingrich (who has won only one), has more delegates, and leads him in the polls. In at least one poll, he also leads Romney. It isn’t yet a Romney–Santorum contest, but it could be headed that way.

We hope so. Gingrich’s verbal and intellectual talents should make him a resource for any future Republican president. But it would be a grave mistake for the party to make someone with such poor judgment and persistent unpopularity its presidential nominee. It is not clear whether Gingrich remains in the race because he still believes he could become president next year or because he wants to avenge his wounded pride: an ambiguity that suggests the problem with him as a leader. When he led Santorum in the polls, he urged the Pennsylvanian to leave the race. On his own arguments the proper course for him now is to endorse Santorum and exit.

Santorum has been conducting himself rather impressively in his moments of triumph and avoiding characteristic temptations. He is doing his best to keep the press from dismissing him as merely a “social-issues candidate.” His recent remark that losing his Senate seat in 2006 taught him the importance of humility suggests an appealing self-awareness. And he has rightly identified the declining stability of middle-class families as a threat to the American experiment, even if his proposed solutions are poorly designed. But sensible policies, important as they are, are not the immediate challenge for his candidacy. Proving he can run a national campaign is.

Romney remains the undramatic figure at the center of the primaries’ drama. Lack of enthusiasm for him has set it all in motion. Romney is trying to win the nomination by pulverizing his rivals. His hope is that enthusiasm will follow when he takes on Obama in the summer and fall. But his attacks on Santorum have been lame, perhaps because they are patently insincere. (Does anyone believe that Romney truly thinks poorly of Santorum’s votes to raise the debt ceiling?)

Romney is a transactional politician rather than a charismatic one. Maybe he should make the most of it: Tell conservatives what they will get out of a Romney presidency. Entitlements brought under budgetary control. A more market-oriented health-care system. Judges who know their place in the constitutional architecture. Fannie and Freddie extinguished. The defense budget protected. Tax reform, and tax relief for families. In some cases making this case will require that Romney commit to more detailed proposals than he has thus far; in others that he will do more to emphasize things he has already said. But emphasis and repetition are not trivial in presidential campaigns. So far Romney has been running mostly on his biography: Republicans are supposed to vote for him because he is a family man and shrewd businessman. And Republicans, even the many who are well disposed to him, have been saying as loud as they can: It isn’t enough.