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In a sketch last weekend following Mitt Romney's win in Michigan, "Saturday Night Live" had its Romney character boast that it was another instance of voters saying of him, "Eh, I guess."

"Eh, I guess" looks to be the motto he'll have to try to ride to the nomination. It was an "eh" night for Romney, although he avoided catastrophe by pulling out a razor-thin win in Ohio where he was trailing most of the night.

Otherwise, he won one state where he used to be governor (Massachusetts), a small Northeastern state (Vermont), an essentially uncontested Southern state (Virginia),  a heavily Mormon state out West (Idaho) and Alaska. In Virginia, he couldn't get to 60 percent against just Ron Paul. Rarely has a candidate seemed so inevitable and so weak at the same time.

Romney has always been the default candidate, dependent on discrediting the other candidates or having them discredit themselves before Republican voters turn to him. His two biggest initial threats, Rick Perry and Newt Gingrich, were highly vulnerable and either disappeared or rapidly diminished. Santorum looked like he was headed for the same fate, but has proven more resilient.

His performance has been amazing given Romney's advantages. Romney is the only candidate who has bothered to or been capable of running a traditional presidential campaign. He built an organization, raised money, ran an opposition research shop, and garnered endorsements. He has relied on this machinery to see him through what has turned out to be more of a grind than he ever expected.

Santorum, in contrast, has been building a campaign on the fly and is still something of a one-man band. He has been badly out-spent and out-organized. On the most important night of the Republican nomination battle so far, Santorum wasn't even on the ballot in Virginia and left delegates on the table in Ohio by not filing slates in all congressional districts.

Yet he has significant strengths. He is bonded with evangelicals. It's no accident that he won two states (Tennessee and Oklahoma) where more than 70 percent of Republican voters were evangelicals. (He also won the North Dakota caucuses, where there weren't exit polls.) Santorum's base is the core of the base of the Republican party. In Tennessee and Oklahoma, very conservative voters and strong supporters of the Tea Party were a plurality of all voters and Santorum won them handily.

By any standard, Santorum has had a rocky couple of weeks of messaging. He's gotten embroiled in unnecessary controversies and regretted his choice of words.

But none of it has dented his authenticity, the quality that contrasts him most with Romney. No one writing a political science textbook would ever recommend running a campaign the way Santorum does--on gut instinct and without ever delivering a speech that is written down. What he loses in crispness by this approach he gains in sincerity.

Santorum surely would have won Georgia as well if it weren't for Newt Gingrich. The former speaker won his home state, but picking off a few Southern states and finishing third or fourth everywhere else is emphatically not a formula for winning the nomination. Gingrich finished third in Tennessee and Oklahoma. The irony is that he seems motivated, in part, by a revenge fantasy against Mitt Romney, but his continued presence in the race is one of Romney's best tools against Santorum since he splits the conservative vote.

In Ohio, Gingrich got 15 percent of the vote, no doubt a store of potential Santorum voters. Romney was able to pull out the state because the electorate was almost divided in even thirds among very conservatives, somewhat conservatives and moderates. Romney won by almost 2-1 among those 42 percent of voters who said the ability to beat Obama is the most important voter quality. He beat Santorum by 8 points among the 54 percent of voters who say they care most about the economy.

A clear demographic split was evident in Ohio. Santorum won non-college graduates and Romney college graduates. Santorum won voters making less than $100,000, Romney voters making more than $100,000. This speaks to a weakness with the working class that could hurt Romney in the fall if he's the nominee.

He's got to get to 1,144 delegates first. He has a clearer path there than anyone else, but it will continue to be a rocky one. Shaky in the Midwest and extremely weak in the South, Romney can't relish the prospect of coming contests in Kansas, Alabama, and Mississippi. For all his technical proficiency and institutional advantages, Romney so far is the candidate of "eh."

Rich Lowry is editor of The National Review and a Fox News contributor.