WASHINGTON – After every other conservative alternative to Mitt Romney crashed and burned (libertarian Ron Paul is in a category of his own), from the rubble emerges Rick Santorum. But he isn’t just the last man standing. He is the first challenger to be plausibly presidential: knowledgeable, articulate, experienced, of stable character and authentic ideology.

He’d been ignored largely because he appeared unelectable – out of office for five years, having lost his Senate seat in Pennsylvania by a staggering 17 points in 2006.

However, with his virtual tie for first in Iowa, he sheds the loser label and seizes the momentum, meaning millions of dollars’ worth of free media to make up for his lack of money. He’s got the stage to make his case, plus the luck of a scheduling quirk: If he can make it through the next three harrowing primaries, the (relative) February lull would allow him to build a national campaign structure before Super Tuesday on March 6.

Santorum’s electoral advantage is sociological: His common-man, working-class sensibility would be highly appealing to battleground-state Reagan Democrats. His fundamental problem is ideological: He’s a deeply committed social conservative in a year when the country is obsessed with the economy and when conservatism is obsessed with limited government. Republicans, after all, swept the 2010 election on economic concerns and opposition to big government. The tea party revolution was not about gay marriage. Which is why so much tea party fervor attaches to Paul.

Santorum did win the tea party vote in Iowa. But because he was such a long shot, his record did not receive much scrutiny. It will now. He is no austere limited-government constitutionalist. He participated in George W. Bush’s compassionate conservatism, which largely made peace with big government. Santorum, for example, defends earmarks and supported No Child Left Behind and the Medicare prescription drug benefit. It’s a perfectly defensible philosophy – but now he’ll be called upon to actually defend it.

Moreover, Iowa is anomalous. It’s not just that the Republican electorate is disproportionately evangelical and thus highly receptive to Santorum’s social conservatism (as to Mike Huckabee’s in 2008). It’s that Iowa’s economy is unusually healthy with only 5.7 percent unemployment, high agricultural prices and strong real estate values. Although the economy did rate as a major issue in the entrance poll, in such relative prosperity it registers more as a concern for the nation than as a visceral personal issue – diminishing the impact of Romney’s calling card, economic competence.

For his part, Romney remains preternaturally inert. His numbers, his demeanor, his campaign are flat-line steady: no highs, no lows, no euphoria, no panic.

With one minor exception. Romney wasn’t expected to do very well in Iowa. A top-three finish would have been good; a first or second, a surprising success. But feeling his Iowa prospects rise, he let fly a last-minute high. (Two hairs were seen dangling over his forehead.) He began touting his chance of winning, thus gratuitously raising expectations.

That turned a hairline victory into something of a setback, accentuating his inability to break out of his flat-line 25 or so percent support. How flat? His final 2012 Iowa vote count deviated from his 2008 total of 30,021 by six votes. (Not six percent. But a party of six.)

For a front-runner who can’t seem to expand his base, he’s been fortunate that the opposition has been so split. But the luck stops here. Michele Bachmann is gone. Rick Perry will skip New Hampshire, then dead man walk through South Carolina. And then there is Newt.

Gingrich is staying in. This should be good news for Romney. It’s not. In his Iowa non-concession speech, Gingrich was seething. He could not conceal his fury with Paul and Romney for burying him in negative ads. After singling out Santorum for praise, Gingrich launched into them both, most especially Romney.

Gingrich speaks of aligning himself with Santorum against Romney. For Newt’s campaign, this makes absolutely no strategic sense. Except that Gingrich is after vengeance, not victory. Ahab is loose in New Hampshire, stalking his great white Mitt.

What a lineup. Santorum and Gingrich go after Romney, whose unspoken ally is Paul, who needs to fight off Santorum in order to emerge as both No. 1 challenger and Republican kingmaker, leader of a movement demanding respect, attention and concessions. And Jon Huntsman goes after everybody.

Is this any way to pick a president? Absolutely. It works. It winnows. And it has produced, after just one contest, an admirably worthy conservative alternative to Romney.

© 2012, The Washington Post Writers Group