He writes in the Washington Post:

...Rick Santorum has become central because Iowa Republicans ignored an axiom that is as familiar as it is false: Democrats fall in love, and Republicans fall in line. Republicans, supposedly hierarchical, actually are — let us say the worst — human. They crave fun. Supporting Mitt Romney still seems to many like a duty, the responsible thing to do. Suddenly, supporting Santorum seems like a lark, partly because a week or so ago he could quit complaining about media neglect and start having fun, which is infectious.

... White voters without college education — economically anxious and culturally conservative — were called “Reagan Democrats” when they were considered only seasonal Republicans because of Ronald Reagan. Today they are called the Republican base.

Who is more apt to energize them: Santorum, who is from them, or Romney, who is desperately seeking enthusiasm?