BIRMINGHAM, Ala. (AP) - Mitt Romney is working to seal his status as the Republican presidential front-runner with a thus-far-elusive victory in the Deep South.
Closely fought primaries in Alabama and Louisiana offer the former Massachusetts governor a key opportunity in a region that has been slow to embrace him.
Tuesday's primaries are also poised to render a possible final verdict on Newt Gingrich's Southern-focused candidacy.
With polls showing an unexpectedly tight race in the conservative bellwether states, Romney made a campaign appearance Monday in Alabama - a clear indication he was eyeing a potential win there.
Romney campaigned with Southern comedian Jeff Foxworthy and poked fun at his own lack of hunting skills, saying he hoped to set out with an Alabama friend who "can actually show me which end of the rifle to point."
Battling anew to be Romney's main conservative challenger, Gingrich and Rick Santorum both spoke at an energy forum in Mississippi and took questions on religion in public life at a presidential forum in Birmingham, Ala.
They took sharp aim at President Barack Obama, with Santorum labeling the president's foreign policy "pathetic" and Gingrich taunting Obama as "President Algae" for an energy speech in which Obama spoke of research that would allow oil and gas to be developed from algae one day.
Gingrich has focused his campaign in recent weeks on rising gas prices, promising to bring the price to $2.50 per gallon if elected.
The Southern showdown came as new polling showed a steep drop in Obama's approval ratings amid escalating prices at the pump and renewed turbulence in the Middle East.
A Washington Post-ABC News poll found that 46 percent of those surveyed approve the way the president is handling his job, and 50 percent disapprove.
A New York Times/CBS poll found 41 percent approval, and 47 percent disapproval.
A win in either Mississippi or Alabama would be an important breakthrough for Romney, easing concerns that the Harvard-educated Northeasterner cannot win the party's most conservative and evangelical voters.
Romney did not plan to be in the state during voting Tuesday and was already looking ahead to contests in Missouri on Saturday and Puerto Rico on Sunday.
Santorum, who has angled to campaign head-to-head with Romney, pressed the case again that Gingrich should consider stepping aside.
"People of Mississippi and Alabama want a conservative," he told reporters in Biloxi. "If they want a conservative nominee for sure, they can do that by lining up behind us and making this race clearly a two-person race outside of the South."
Santorum planned to watch returns from Louisiana, which holds its primary March 24.
He was also heading to Puerto Rico to campaign later in the week. While Gingrich insists he plans to remain in the race until the Republican National Convention in August, his campaign's survival essentially rested on winning both Tuesday contests.
The former House speaker has pursued an all-Southern strategy, but he has won only South Carolina and Georgia, the latter the state he represented in Congress for 20 years.
Gingrich planned several appearances in Alabama on Tuesday, including remarks to a local chamber of commerce and a visit to the Birmingham Zoo.
He seemed to draw new energy from an enthusiastic crowd at Birmingham forum.
They gave him repeated standing ovations as he derided Obama for offering apologies earlier this month to Afghan President Hamid Karzai after American troops burned Islamic holy books, including some Qurans.
"He believes in apologizing to those who kill our young men and women. I will never apologize," Gingrich said to applause and cheers of "Newt! Newt! Newt!"
All three candidates were receiving support from well-heeled independent groups known as super PACs that were helping to finance television ads, automated phone calls and direct mail in the two states.
A fourth candidate, Texas Rep. Ron Paul, was not competing actively in the two contests.
Hawaii was also holding a primary Tuesday, but none of the GOP hopefuls campaigned there.
Romney 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.
The Associated Press tally shows him with 454 of the 1,144 delegates needed to win the nomination. Santorum has 217, Gingrich 107 and Paul 47.
Associated Press writers David Espo in Washington and Philip Elliott in Montgomery, Ala., contributed to this report.