Former Pennsylvania senator Rick Santorum won the primaries in Alabama and Mississippi on Tuesday, potentially knocking former House Speaker Newt Gingrich out of the race, and potentially reshaping the GOP 2012 contest.

Gingrich, who has struggled since a victory in South Carolina in January, had hinted he would consider leaving the race if he didn’t win in either Alabama or Mississippi, although he pledged on Tuesday night to continue his campaign. He had previously described the Deep South as the base of his support and a region in which he could win.

If Gingrich drops out in the next few days, it would give Santorum what he has long craved: effectively a one-on-one contest with former Massachusetts governor Mitt Romney, with Rep. Ron Paul (R-Tex.) still in the race but so far unable to galvanize enough support to win in any state.

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Romney, who entered the night with a lead of more than 200 delegates over Santorum, is still far ahead of his competitors. And Santorum may not even gain on Romney in the delegate count from Tuesday when results from Hawaii and American Samoa, both of which held caucuses late Tuesday, are taken into account.

Romney won both contests.

But the losses in the South by Romney illustrate his continued struggles with the base of the GOP, and will embolden Santorum to continue running through this spring and potentially into June. The exit poll in Alabama showed that, among voters who called themselves “very conservative,” Santorum collected 41 percent of the vote, Romney 18 percent.

The Republican race now heads to Missouri, which will hold caucuses on Saturday, then a primary in Illinois on Tuesday. Santorum, who has done well in caucuses in the Midwest, is the favorite in Missouri, while Illinois is a large state full of moderate Republicans where Romney is likely to do well.

But if Gingrich departs, Santorum could have a new opening. He and Gingrich have split the votes of the evangelical, very conservative, and Tea Party blocs of the GOP, all of which have been hesitant to back Romney. If Santorum consolidates those blocs, he could potentially win and collect more delegates in states like Louisiana, which holds a primary on March 24.

Follow Perry Bacon Jr. on Twitter at @perrybaconjr