Story highlights Rick Santorum has moved up quickly in the Iowa polls; caucuses are Tuesday

Alex Castellanos says a strong finish would give Santorum a shot at the national stage

He says it would be crucial for Santorum to stress the economic side of his message

Castellanos: If Santorum only appeals to social conservatives, his candidacy would be over

Tuesday night, after the results of the Iowa caucuses are in, Rick Santorum could well confront the 10 most important minutes of his political life.

Iowa is not the Super Bowl; it's a playoff game. If Santorum exceeds expectations and finishes in the top three, close to Ron Paul and Mitt Romney, he will have earned no more than the right to compete again.

He'll have succeeded, not because his old-school, retail campaign worked, but because it kept him hidden. Santorum's noncampaign for the Republican presidential nomination kept him in suspended animation, to awaken only after every other anti-Romney candidate had burned bright and then melted under the campaign's magnifying heat. Santorum will only have outlasted Michele Bachmann, Rick Perry and Newt Gingrich, not beaten them.

Even as he surges in Iowa, Santorum remains at 5% in Gallup's national tracking polls. And from here it gets harder. All Santorum will really have won is this: A few minutes Tuesday evening to stand alone on the national stage and introduce himself as the candidate who could become the choice of Republicans looking for an alternative to Mitt Romney.

Alex Castellanos

How he handles this first impression will determine whether he grows into a serious national contender or Romney's dream opponent, a placeholder with no chance of moving into the top ranks.

There is a model for what Santorum should not do. It's Bachmann's campaign. After winning the Iowa Straw Poll in August, Bachmann never fought her way out of the State Fairgrounds. She remained a narrow, evangelical conservative competing for the church vote in Iowa, not the large, national constituency concerned that President Barack Obama is flushing their economy down a drainpipe. The night of her Iowa victory was actually the end of her campaign, not the beginning. There is no need for Santorum to repeat Bachmann's mistake.

There will be voices in his ear whispering bad advice. They will urge, "Rick, go to South Carolina. You can't win New Hampshire. There aren't enough evangelicals."

JUST WATCHED Will Santorum win in Iowa? Replay More Videos ... MUST WATCH Will Santorum win in Iowa? 04:07

JUST WATCHED The Santorum surge Replay More Videos ... MUST WATCH The Santorum surge 02:54

JUST WATCHED Santorum breaks down in Iowa Replay More Videos ... MUST WATCH Santorum breaks down in Iowa 01:21

JUST WATCHED Three-way battle for lead in Iowa Replay More Videos ... MUST WATCH Three-way battle for lead in Iowa 02:35

If he listens, the national news media will assume Santorum's campaign, like Bachmann's, has admitted the prospects of broadening his appeal and actually getting nominated, much less beating Obama, are nonexistent.

If Rick Santorum believes he can't compete beyond the pews, why should anyone else? A Santorum who focuses on both social issues and the economy will end up being defined only by social issues. The media will go where the drama is and ask him a million questions about abortion, gay marriage and every other social issue this election isn't about. No one will hear his economic message. Wednesday, even as large crowds cheer him in South Carolina, Santorum's campaign will be dead.

Instead, Tuesday night, Santorum should invite reporters to ride along; he's catching the morning bus to New Hampshire. The fight to renew this great nation's economy begins there.

Santorum has a pretty good rap on the economy. He's the candidate of the America worker, not just the American investor. On the stump, Santorum explains he's the son of an Italian immigrant and his grandfather worked in coal mines. Santorum can sing a legitimate working-class anthem; it is in his family's blood. He's represented it in Congress. He know that cities such as Pittsburgh, his home, are what steel mills really built.

On his website, the remaining Republican candidate most likely to have a beer with you, or without you, explains, "Unlike President Obama's faith in top-down government control, Rick Santorum believes in the power of the American worker to once again make our economy the envy of the world."

Earth to Santorum: Go to New Hampshire. Take on Obama's elitism. Let the world know you are talking only about the economy for the next month, because unless we rescue our economy from the Obama's Washington experts and pull the American worker back from the economic precipice, nothing else matters.

Tuesday night, face forward. You'll have 10 minutes.