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 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.

He can, of course, be tenaciously serious. On Sept. 26, 1996, the Senate was debating whether to ban partial-birth abortion, the procedure whereby the baby to be killed is almost delivered, feet first, until only a few inches of its skull remain in the birth canal, and then the skull is punctured, emptied and collapsed. Santorum asked two pro-choice senators opposed to the ban, Russ Feingold, D-Wis., and Frank Lautenberg, D-N.J., this: Suppose the baby slips out of the birth canal before it can be killed. Should killing it even then be a permissible choice? Neither senator would say no.

On Oct. 20, 1999, during another such debate, Santorum had a colloquy with pro-choice Barbara Boxer, D-Calif.:

Santorum: “You agree that, once the child is born, separated from the mother, that that child is protected by the Constitution and cannot be killed. Do you agree with that?”

Boxer: “I think that when you bring your baby home …”

Santorum is not, however, a one-dimensional social conservative. He was Senate floor manager of the most important domestic legislation since the 1960s, the 1996 welfare reform. This is intensely pertinent 15 years later, as the welfare state buckles beneath the weight of unsustainable entitlement programs: Welfare reform repealed a lifetime entitlement under Aid to Families with Dependent Children, a provision of the 1935 Social Security Act, and empowered states to experiment with new weaves of the safety net.

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?

Romney recently gave a speech with a theme worthy of a national election, contrasting a “merit-based” or “opportunity” society with Barack Obama’s promotion of an “entitlement society,” which Romney termed “a fundamental corruption of the American spirit”: “Once we thought ‘entitlement’ meant that Americans were entitled to the privilege of trying to succeed. … But today the new entitlement battle is over the size of the check you get from Washington. … And the only people who truly enjoy any real rewards are those who do the redistributing – the government.”

Romney discerns the philosophic chasm separating those who embrace and those who reject progressivism’s objective, which is to weave a web of dependency, increasingly entangling individuals and industries in government supervision. Santorum exemplifies a conservative aspiration born about the time he was born in 1958. Frank Meyer, a founding editor of William F. Buckley’s National Review in 1955, postulated the possibility, and necessity, of “fusionism,” a union of social conservatives and those of a more libertarian, free-market bent.

If the Republicans’ binary choice has arrived, and if new technologies of communication and fundraising are repealing some traditional impediments to fluidity in political competition, Santorum can hope to win the nomination. Yes, in 2006, a ghastly year for Republicans (who lost 30 seats and control of the House, and six Senate seats), Santorum lost by 17 points in his bid for a third term. But, then, Richard Nixon was defeated for governor of California six years before being elected president, carrying California.

Even if Santorum is not nominated, he might galvanize a constituency that makes him a vice presidential choice. For Obama, getting to 270 electoral votes without Pennsylvania’s 20 is problematic. But so, just now, are Republican prospects of getting to 270 with their narrowing choice of candidates.