Santorum once again proved his viability as Romney's chief rival this past Tuesday when he won the Alabama and Mississippi primaries. The Santorum victory further marginalized Newt Gingrich, who was banking on Southern wins, and again raised questions about Romney's appeal in traditionally conservative areas of the country. 

Romney, though, walked away with more delegates than Santorum on Tuesday -- by winning contests in Hawaii and American Samoa, and peeling off some of the Southern state delegates. 

The candidate has been on a seemingly steady march toward the 1,144 delegates needed to clinch the nomination, though it's unclear whether his rivals might be able to deprive him of that threshold come the convention. 

A set of Santorum victories in the coming four contests would likely invigorate his campaign going in April, when big states like New York and Pennsylvania weigh in.