There's an old saying that Republicans don't fall in love, they fall in line. And sooner or later, they'll probably align for Mitt Romney.

But not just yet. With the Iowa caucuses in the rearview mirror and New Hampshire dead ahead, it's early days. This is the point in the GOP calendar when insurgent underdogs bark loudly at the establishment candidates - and sure enough, Rick Santorum is assailing Romney as "bland" and "boring," while Newt Gingrich is vowing to go Shakespearean on Romney by crying havoc and unleashing the dogs of war.

But neither of those guys has the requisite money or organization to take down Romney over the long haul. Grassroots Republicans may find Romney hard to love - indeed, the polls say that 75 percent of them are still holding back, just as 75 percent of Iowa caucus-goers chose other suitors - but odds are they will grudgingly come around, swayed in the end by his electability.

How ironic it is that, in an era of right-wing ideological fervor, the Republican most positioned to win the nomination is not particularly ideological or fervent. At a time when grassroots conservatives are hungry for a fiery unconventional savior, Romney is a conventional candidate with a vanilla sensibility. No wonder they remain hesitant.

Tuesday's Iowa results can be read two ways. Romney and his allied groups dumped roughly $4 million into a state where $4 million goes a long way - yet he wound up with six fewer votes than he received in the '08 caucuses. Santorum spent a pittance by comparison, yet he virtually matched Romney's tally. Clearly, most conservatives still suspect that Romney's rightward rhetorical journey is born of calculation rather than conviction, that his heart and theirs do not beat in unison.

On the other hand, he emerged victorious, albeit by only eight votes, in a contest that is often cruel to establishment Republicans. In 1988, George H.W. Bush finished behind evangelical firebrand Pat Robertson (Bush won the nomination); in 2008, John McCain finished far behind the winner, religious-right favorite Mike Huckabee (McCain won the nomination). But Romney won Tuesday because a thin plurality of Iowans tapped their heads rather than their hearts and saw him as the best hope for November. And, for the same reason, he'll likely win New Hampshire this Tuesday.

But he'll take some heavy hits this month, as Gingrich and Santorum double down on their claim that he's a phony conservative. (Rick Perry is still hanging around, too, although at this point nobody listens to him.) Gingrich calls Romney a "Massachusetts moderate," thereby signaling that Massachusetts will replace San Francisco as a GOP pejorative, but the former speaker is not really a serious threat anymore. He's just ticked off that Romney's allies buried him with TV attack ads in Iowa, and now he's thirsting for revenge. So much for the New Newt, the calm, statesmanlike image that lasted roughly three weeks. The petulant Newt is the real Newt, and that wore people out 15 years ago.

Santorum, buoyed by new donations flowing his way, figures to be a more substantive counterweight to Romney (until Romney presumably grinds him down, state by state). Unlike Romney, he viscerally connects with blue-collar Catholics in the Rust Belt. His purist pedigree, particularly on social issues, could click with conservative primary voters who suspect that Romney is just reading the lines without feeling the music. And Santorum's populist biography (son of an Italian immigrant) trumps Romney, who grew up rich.

In the short run, Santorum can potentially damage Romney - and delight President Obama's campaign team - by painting Romney as a weather vane who dumped his moderate gubernatorial beliefs to remarket himself for a more conservative electorate. We'll also hear more about how Romney's Massachusetts health overhaul served as a template for Obama's law (which is true). In Santorum's words, this battle will pit the "bold" against the "bland."

But Santorum may soon yearn for the days when nobody paid attention to him, because now comes the scrutiny. Romney's flaws have long been out there. Santorum has his own, abundant flaws, and he'll be forced to defend against them. For instance, it's fine to tell conservatives that "any doctor who performs an abortion should be criminally charged" and that he opposes contraception because "it's a license to do things in the sexual realm," but in what universe can a Republican nominee say such things and still expect to score big with female voters? (He's already playing defense on contraception; on Wednesday he said, "I don't believe that everything that is immoral should be illegal.")

We're talking here about electability. It's also an open question whether swing voters would embrace Santorum's demagoguery about Obama - such as when he accuses the president of "absolutely un-American activities" and says the president "has actively embraced those who do us harm." Swing voters may be frustrated with Obama, but they won't necessarily ingest the red meat about Obama being treasonous. That's a tough charge to level against a guy who has whacked a string of al-Qaeda terrorists.

But let's not get ahead of ourselves. The key audience right now is composed of conservative primary voters, many of whom hate government - and there was Santorum, a 16-year Washington politician who routinely did business with the K Street lobbyists, who voted for the expensive (unpaid for) Medicare prescription-drug coverage law, who voted for the infamous '05 highway law that featured thousands of porky earmarks, including the Bridge to Nowhere. So he's not so pure, either. Romney, if he so chooses, can credibly tag Santorum as a career Washington insider.

Santorum at best may succeed in nudging Romney further rightward, but the thing is, Romney is essentially there already. He wants to end Medicare as we know it, he wants to "get rid of" federal expenditures such as Amtrak and public television, he repeats the canard that Obama travels the globe apologizing for America, and so much more. Regardless of whether conservatism burns in his heart, Romney would be compelled, by the pressures within his party, to govern on the right.

And when primary-season passions are extinguished, I suspect that most Republicans will fall in line. It's no cinch to beat an incumbent who's sitting on a billion in cash, and only the strongest player in a weak Republican field will be up to the task.

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