Published for www.washingtonpost.com, February 16, 2012

The central narrative of the Republican nomination contest is easy to summarize: Any candidate who is perceived as the main opponent to Mitt Romney immediately ties or leads Mitt Romney.

Rick Santorum’s surge tracks with recent precedent. His support is about the same as Rick Perry’s at his peak. A little higher than Herman Cain’s crest. A little lower than Newt Gingrich’s pinnacle.

But Santorum is not only Romney’s latest challenger, he is the most serious. Perry did not possess presidential-level skills. Cain lacked any apparent qualification for high office. Gingrich managed to systematically confirm every doubt about his style and stability.

Santorum, in contrast, has shown the ability to learn. While his initial debate performances were peevish and unappealing, he has grown more confident and likable over time. He has effectively prosecuted Romney’s public record while avoiding anger or overreach. (He pointedly refused, for example, to attack Romney’s business achievements and personal wealth.)

The former Pennsylvania senator possesses strengths that neatly fit some of Romney’s weaknesses. Santorum combines a deeply held social conservatism with an authentic blue-collar appeal. Romney has trouble competing in either category. While Santorum is very conservative, he avoids being a conservative caricature. He was one of the Senate’s main advocates of global health programs and a champion of faith-based anti-poverty efforts.

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