Mitt Romney has been declared the winner of the Ohio GOP primary. As the Fix team explained:

Former Massachusetts governor Mitt Romney defeated former senator Rick Santorum of Pennsylvania on Tuesday in Ohio, taking the marquee contest of the evening. The race was close throughout the night and wasn’t called until after 12:30 a.m. Eastern time, capping a successful Super Tuesday for Romney’s campaign in which he won at least five states.

The narrow result left the political world uncertain about the direction of the national race. A Romney victory, it was thought, would cement him as the clear favorite in the Republican primaries. A Santorum win would allow him to claim real momentum.

Santorum had led in the Buckeye State for the better part of the past month, but Romney began to close the gap in the final week as a result of heavy spending on television ads and a bit of momentum earned from victories in Arizona and Michigan on Feb. 28. Ohio is the only Super Tuesday state where Romney and Santorum went head-to-head that is likely to be seriously contested in the fall campaign. That swing-state status raised its profile, with the state regarded as an indicator of which of the two Republican candidates would be better positioned to take the fight to President Obama in the fall.

So important was Ohio that Santorum gave his victory speech — he won in Oklahoma and Tennessee — in Steubenville. Romney stumped in the state before flying to his Boston campaign headquarters to monitor election returns.

Polling analysis from Behind the Numbers:

Mitt Romney narrowly edged Rick Santorum in Ohio, the biggest prize of Super Tuesday, splitting the Republican electorate along now familiar ideological and religious lines.

Nearly three in four of Santorum’s votes in Ohio came from social conservatives; in fact, 58% of his voters described themselves as very conservative on these issues. Nearly six in 10 of Santorum’s voters said Romney is insufficiently conservative. And in a sign of potential trouble ahead, 58 percent of Santorum’s backers in Ohio say they’d be dissatisfied with Romney as the nominee; 55 percent of Romney’s supporters say same about Santorum atop the GOP ticket.

Romney’s victory in Ohio is due in part to increased turnout among wealthier voters. About three in 10 voters had family income of $100,000 or more with nearly half picking Romney. Rick Santorum ran ahead of Romney among voters with incomes below $100,000 and those without a college degree.

Analysis from The Fix: Think Michigan was fun? Welcome to Ohio. Ohio gets top billing because the campaigns have been spending the most money on ads here, Ohio has the second-most delegates at stake, and it’s a Midwestern state where it’s anybody’s ball game. But mostly, it’s because this is the biggest test for Mitt Romney, with the other three big primary states all residing south of the Mason-Dixon line.

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