(CNN) -- Republican front-runner Mitt Romney declared himself a bit of an outsider Thursday in the upcoming GOP primaries in Mississippi and Alabama, while Rick Santorum battled to emerge from the heart of Dixie as the surviving conservative challenger.
The two states are holding their presidential primaries Tuesday, along with caucuses to be held in Hawaii and American Samoa. Voters in Kansas and the Virgin Islands weigh in on Saturday.
Mississippi and Alabama have the potential to play a key role in the race. Former House Speaker Newt Gingrich, running well back of Romney and Santorum so far, recently canceled plans to stump for votes in Kansas and is focusing all of his attention on the two Deep South states.
Gingrich campaign spokesman R.C. Hammond told reporters Wednesday the former speaker -- who has only won South Carolina and his home state of Georgia so far -- needs to carry both states to remain a credible candidate.
The Gingrich campaign took aim at Santorum on Thursday with a new web video that depicted the former Pennsylvania senator as a big-spending Washington politician.
"Sen. Santorum poses as fiscally responsible, but he's the one who broke the bank while in Senate leadership," Joe DeSantis, the communications director for Newt 2012, said in a news release. "... As the poster child of the big government Republican Party that the American people rejected in 2006 and 2008, Sen. Santorum ... cannot offer the stark choice we need between President Obama's big-spending record."
Santorum, campaigning in Huntsville on Thursday, urged Alabama voters to help turn the contest into a two-man race between himself and the more moderate Romney, who has a big lead in delegates but continues to have trouble winning strong conservative support.
In many races so far, combining the support for Santorum and Gingrich would exceed the support for Romney, causing increased calls for one of the two conservative challengers to drop out.
"If you go out and deliver a conservative victory for us on Tuesday, this race will become a two-person race," Santorum said. "And when it becomes a two-person race for the Republican nomination, the conservative will win that nomination."
A pro-Santorum super PAC -- the Red, White and Blue Fund -- launched a Mississippi and Alabama ad buy Thursday worth as much as $600,000. The ad criticizes both Romney and Gingrich for their past stances on the politically contentious issue of health care reform.
Despite his primary wins and growing delegate lead, Romney has repeatedly shown weakness with Southerners, evangelicals and other voting blocs that make up the GOP base.
The former Massachusetts governor acknowledged during an interview Thursday with an Alabama radio host that the state's upcoming contest is "a bit of an away game."
But "I am confident we are going to get some delegates," he said "That's, of course, what this is all about."
He later told a crowd in Pascagoula, Mississippi, that he was starting to become more of a Southerner.
"I am learning to say 'y'all' and I like grits, and things, strange things, are happening to me," Romney joked.
According to CNN's latest count, Romney now has 429 delegates, compared with 169 for Santorum, 118 for Gingrich and 67 for Rep. Ron Paul of Texas. A candidate needs 1,144 delegates at the Republican convention this summer to secure the nomination to face President Barack Obama in November.
Romney significantly expanded his margin in the delegate hunt this week, carrying six of the 10 states up for grabs on Super Tuesday.
"Super Tuesday dramatically reduced the likelihood that any of Gov. Romney's opponents can obtain the Republican nomination," said Rich Beeson, the campaign's political director. "As Gov. Romney's opponents attempt to ignore the basic principles of math, the only person's odds of winning they are increasing are President Obama's."
Among other things, Beeson noted there are now few major delegate prizes remaining, and that most of the states yet to vote have rules requiring a proportional allocation of delegates -- a reality that makes it hard to narrow Romney's lead.
"We think that will get done before the convention," Romney said in a CNBC interview Wednesday. "One thing I can tell you for sure is there's not going to be a brokered convention where some new person comes in and becomes the nominee. It's going to be one of the four people that are still running."
For their part, Santorum and Gingrich insist there is still an anti-Romney majority within the Republican Party that can unify in the weeks ahead.
"What Romney is trying to do is call the game before it's even halftime because he has a lead," Santorum adviser John Brabender said Wednesday, reacting to Beeson's argument about the delegate tally.
Romney wants to "disenfranchise Republican primary voters," Brabender asserted.
Former candidate Herman Cain, who has campaigned with Gingrich in recent weeks, also said it was premature to talk of anyone pulling out.
"Folks, only ⅓ of the delegates have been allotted! It's too soon to call on a candidate to withdraw from the race!" Cain posted on Twitter.
CNN's Kevin Bohn, Jim Acosta, Mark Preston and Rachel Streitfeld contributed to this report.