COLUMBIA, S.C. - Newt Gingrich didn't just beat Mitt Romney in Saturday's South Carolina primary, the former House speaker kicked away one of the main pillars of his rival's election campaign.

Republican US presidential candidate and former House Speaker Newt Gingrich with wife Callista (R) laughs in front of cameras at his South Carolina Primary election night rally in Columbia, South Carolina, January 21, 2012. [Photo/Agencies]

Exit polling data shows Gingrich convinced voters he would be the toughest Republican opponent against President Barack Obama in the November general election.

Electability - Republican campaign-speak for a candidate's ability to beat Obama - had been one of Romney's top selling points until Saturday.  

Conventional wisdom was that the former Massachusetts governor's emphasis on jobs and the economy and his perceived appeal to independents would help him against Gingrich, who is often seen as erratic and divisive.

But Gingrich's combative style in debates resonated with voters keen for a heavyweight debater to take on Obama, who is grudgingly respected by Republicans as a formidable campaigner.  

This may also be helping Gingrich's message on the economy gain traction, exit polling data showed.

South Carolina's Republicans rated the ability to beat Obama as a candidate's most important quality, an exit poll on CNN showed.

Forty-five percent of voters said that was the main attribute they sought in a nominee. Of that group, 51 percent voted for Gingrich compared to 37 percent for Romney.

Twenty-one percent of South Carolina voters said the quality that mattered most to them in their candidate was that he had the right experience.

"It is electability, and that is measured in your ability to effectively debate and prosecute your case against Obama," said Republican strategist Matt Mackowiak.    

Exit polls also showed that for 63 percent of South Carolina voters the most important issue was the economy. Gingrich won this group by a margin of eight percentage points over Romney.

The attraction of Gingrich as an anti-Obama candidate may be the factor that increased his ratings on other issues like the economy, Mackowiak said.

Attacks on Obama in recent weeks, including dubbing him "a foodstamp president," endeared Gingrich to voters in a state with unemployment of almost 10 percent.