(AP) - A resurgent Rick Santorum swept primaries in Alabama and Mississippi Tuesday night, upending the race for the Republican presidential nomination as he sought to push Newt Gingrich toward the sidelines. Mitt Romney was running third in both states. "We did it again," Santorum told cheering supporters in Lafayette, La. He said it was time for conservatives to unite in an effort to defeat Romney, the former Massachusetts governor who is the faraway leader in the competition for Republican National Convention delegates. Romney bristled in the hours before the votes were counted, saying Santorum was "at the desperate end of his campaign." But it was Gingrich with the most to lose as he struggled for political survival in a part of the country he hoped would fuel one more comeback in the unpredictable race to pick an opponent to President Barack Obama. He congratulated Santorum on his victories, and poked at Romney. "If you're the front-runner and you keep coming in third, you're not much of a front-runner," he said in Birmingham, Ala.