BILOXI, Miss. (AP) -- Republican presidential contenders and their super PAC supporters campaigned aggressively on land, through the mail and over the airwaves Monday 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," said Rick Santorum.
But those criticisms were mere warm-up for the candidates going after each other. Gingrich is struggling for survival in Tuesday'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 in a television interview 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. His best showing in a contested primary was 38 percent in Florida.
Hoping to establish a connection with Southerners, the former Massachusetts governor campaigned in Mobile, Ala., with comedian Jeff Foxworthy, whose trademark jokes that begin "You might be a redneck if. ..."
Romney isn't -- he was born in Michigan, educated at Harvard and elected governor of Massachusetts. And he drew laughter from his audience when he poked fun at himself by saying he hoped to go hunting with an Alabama friend who "can actually show me which end of the rifle to point."
"We have a moral responsibility not to spend more than we take in," he says in an ad his campaign ran in both primary states, although not all the commercials were as self-deprecating as his rhetoric or as positive as his on-air message.
Restore Our Future, a super PAC that supports Romney, aired ads critical of Santorum for having voted in Congress to provide federal funding for Planned Parenthood, and attacking Gingrich for supporting action to combat climate change through cleaner sources of energy.
A radio ad the group aired across both states makes use of Santorum's own voice, including him saying in a debate last month that he was proud of the earmarks he has supported and that he had voted for federal education mandates even though they are against his principles.
"But you know, when you're part of the team, sometimes you take one for the team," he says.
The same organization hit Santorum in mail sent to thousands of homes in Alabama.
"Rick Santorum voted with Hillary Clinton to allow felons to vote. Typical behavior from Washington insider," says one mailing, which makes no mention of Romney.
Red, White and Blue Fund, which backs Santorum, was hardly kinder. It aired commercials saying that Romney and Obama "aren't much different" on key issues such as federal spending and supporting a requirement for individuals to purchase health care coverage. That's a reference to a Massachusetts law that Romney signed in his home state that bears similarities to the legislation Obama won from Congress.
Gingrich, who said over the weekend that Romney is the weakest Republican front-runner in nearly a century, is backed by a super PAC airing ads, as well.
His campaign is advertising at lower levels, including a commercial that hits Obama for high gas prices and another that says the president modeled his health care reform plan after the one Romney had enacted in Massachusetts.
The former House speaker also using a recorded phone message from Chuck Norris in Alabama.
"As president, Newt will repeal Obamacare, get rid of Obama's czars, and use commonsense measures, like building the Keystone Pipeline to lower the cost of gas to two and half dollars a gallon," says Norris, whose website notes he is a movie star and World Professional Middle Weight Karate Champion.
Santorum and Gingrich employed different approaches as they campaigned during the day, the former Pennsylvania senator more critical of Romney, while the former House speaker focused his attacks on Obama.
His comment dismissing Obama's concerns about global warming, however, oversimplified the issue. While it's true that plants need carbon dioxide to grow, the gas also is promoting global warming. "For many plants, that's going to more than offset the benefits of carbon dioxide," said David Wolfe, a professor of plant and soil ecology at Cornell University. "If you have a plant that's dead from heat stress, you can give it all the CO2 you want, but it's not going to benefit."
Gingrich, at the same conference, said Obama is presiding over a "very anti-fossil fuel administration. The left wing environmental movement hates oil."
Romney made the economy his text for criticizing Obama.
He said the president wrongly thinks the country is doing better because of recent increases in employment. More than 200,000 jobs have been created in each of the past three months, but Romney said the president, "should go out and talk to the 24 million Americans who are out of work or stopped looking for work or are unemployed."
Associated Press writers Charles Babington, Beth Fouhy, Philip Elliott and Phillip Rawls in Alabama and Stephen Ohlemacher, Kasie Hunt, Seth Borenstein and Jack Gillum in Washington contributed to this story.