Rick Santorum is presenting a stylistic and substantive alternative to Mitt Romney. If he pulls far ahead of the other contenders (with the exception of Ron Paul), as it appears he will do on Tuesday, he will head into South Carolina as the last of the not-Romney candidates still standing. Moreover, he will get there with a substantive message and a resume worthy of a presidential candidate. The man is no Herman Cain.

Polls from South Carolina today do not look encouraging for Santorum. The RealClearPolitics average shows him trailing Romney by double digits. But you can forget about those polls, which still show Newt Gingrich in second place. Gingrich, like Texas Gov. Rick Perry, will do poorly in New Hampshire. That will take the wind out of both of these candidates’ sails. And where do the Perry and Gingrich voters go? Perhaps to Romney, but perhaps in large numbers to Santorum. Those who cheered Perry’s promise not to cut military spending and who relished Gingrich’s defense of Israel simply aren’t going to go over to the Ron Paul camp.

The math may look daunting for Santorum, but consider how fast the other not-Paul and not-Romney candidates are dropping. There will be a majority of the South Carolina electorate up for grabs. Santorum doesn’t need to win there, just to stay on Romney’s heels.

In fact, there’s something to be said just for prolonging the race a bit. As the Hillary Clinton-Barack Obama primary showed, healthy intra-party competition can engage and enliven the base. Moreover, even if Romney wins (still the most likely outcome), it is good practice for him to go up against someone making a working-class appeal.

Romney would do well to talk more about the poor, stress the benefits of his economic plan for working-class (and especially unemployed) Americans and make his economic arguments more accessible to voters. That doesn’t mean changing his positions. (He already, for example, is reserving his proposed capital-gains tax cut for the middle class.) And it doesn’t mean he should try to conceal that he’s had an advantaged life. But he should remember to explain why less regulation benefits manufacturing workers, why free trade is good for the Rust Belt and why the debt is not only an economic problem but a threat to the survival of the American dream.

It is also time for Romney to round out his stance on immigration. Santorum is no pushover and takes a strong law-and-order approach to the border. But he speaks in tones that celebrate the immigrant experience and emphasize how vital it is for America to remain a magnet for those who want to improve their lives. That message has been barely part of Romney’s immigration discussion. He’s got a family immigrant story to tell as well and should use it to good effect.

After a long pre-primary process, the two most thoughtful and knowledgeable candidates have risen to the top. Republicans should welcome that and listen hard to what each has to say. In the end, the party and the eventual nominee will be the better for it.