MONTGOMERY, Ala. (AP) - Alabama's governor hadn't publicly made an endorsement in today's GOP primary -- but today, a spokesman says, Gov. Robert Bentley voted for Rick Santorum. The spokesman says he believes Santorum is "the most conservative candidate" in the race.

Voters in Mississippi are also choosing among the Republican candidates, with polls showing a competitive three-way battle. Mitt Romney hopes for his first victory in the Deep South to seal his status as Republican presidential front-runner. Santorum hopes to knock Newt Gingrich out of the race.

Gingrich is spending the day in Birmingham, Ala., as he waits to see if he can pull off victories today. The future of his candidacy largely rests on today's results. Santorum plans to watch returns from Louisiana, which holds its primary March 24.

Romney has moved on to Missouri. In an outdoor speech in St. Louis today, he ignored his GOP rivals and criticized President Barack Obama's handling of the economy, health care, foreign policy and gasoline prices.

The Southern showdown comes as new polling finds a steep drop in Obama's approval ratings, amid escalating prices at the pump and renewed turbulence in the Middle East.