Rick Santorum turned in his most impressive performance yet with conservative, blue-collar and religious voters as he rode to triumph Saturday in Louisiana 's Republican presidential primary , capturing robust support from people across the board, according to an exit poll of voters.Highlighting his strength, the former Pennsylvania senator bested Mitt Romney for the first time among those calling the economy the campaign's dominant issue. As usual this year, more voters named the economy as their top concern than any other problem and 46 percent of them said Santorum was their candidate — an embarrassment for Romney, the former venture capitalist who has claimed he knows best how to create jobs. Romney retained his usual advantage among voters whose most prized characteristic in a GOP candidate is finding someone who can defeat President Barack Obama this fall. But illustrating the narrowness of the former Massachusetts governor's appeal in the state, 53 percent of ...