Rick Santorum catapulted back into the presidential limelight yesterday, soundly defeating front-runner Mitt Romney in the Minnesota and Colorado caucuses and the symbolic Missouri primary and casting doubt about the former Massachusetts governor’s ability to win over conservatives in the nation’s heartland. Time and again, Romney has tried to vanquish his competition and yesterday’s results was the latest sign that he faces challenges in establishing the broad base of support from his own party as the campaign moves closer to next month’s Super Tuesday.