Heavy GOP campaigning in Alabama, Mississippi

BILOXI, Miss. -- Republican presidential contenders and their supporters campaigned aggressively on land, through the mail and over the airwaves yesterday on the eve of primaries in Alabama and Mississippi with the potential to solidify or shake Mitt Romney's standing as front-runner.

In the Deep South, one of the most conservative regions of the country, Romney and his Republican rivals polished their credentials with attacks on President Barack Obama's handling of the economy and the nation's use of energy.

"The dangers of carbon dioxide? Tell that to a plant, how dangerous carbon dioxide is," Rick Santorum said.

But those criticisms were mere warm-up for the candidates going after each other. Gingrich is struggling for survival in today's primaries, and Santorum is laboring to redeem his claim that Romney can't secure the support of conservatives, particularly evangelicals who are part of the party's key base.

"If the opportunity provides itself in an open convention, they're not going to nominate a moderate Massachusetts governor who has been outspending his opponent 10-1 and can't win the election outright," Santorum said as he campaigned across Alabama and Mississippi.

Romney countered, also on television. "We're closing the deal, state by state, delegate by delegate," he said, emphasizing his lead in the category that matters most.

He has more delegates than his rivals combined, and is amassing them at a rate that puts him on track to clinch control of nomination before the convention opens next summer, a prospect that his rivals prefer not to dwell on.

AP's tally shows him with 454 of the 1,144 delegates needed to win the nomination, Santorum with 217, Gingrich with 107 and Ron Paul with 47.

Evangelical voters play an outsized role in both state primaries. Four years ago, 77 percent of GOP primary voters in Alabama and 69 percent in Mississippi said they were born again or evangelicals, a group that Romney has struggled to bring to his side in the primaries.

Romney's best showing in a contested primary was 38 percent in Florida.