With the Republican presidential nomination still up for grabs after nearly two months of voting, the four remaining candidates will gather for yet another debate tonight in Arizona, the 21st of an unpredictable primary that continues to spring surprise after surprise.
Mitt Romney and Rick Santorum come into the debate in Mesa with the most at stake. The two rivals have been close in polls in the next two states to vote Tuesday - Arizona and Michigan - although Romney has beefed up his lead in the former. For Romney, it is a make-or-break week : Losses in either state, but especially his native state of Michigan, would send shockwaves through the party and position Santorum as the new front-runner heading into Super Tuesday in early March.
The last time Romney entered a debate needing to deliver a strong performance, he did just that. In Florida late last month, Romney outdueled both Santorum and Newt Gingrich en route to an impressive victory in the Sunshine State's Jan. 31 primary. The next week Romney triumphed in the Nevada caucuses , his third win in the first five states to vote, but since then what once appeared an inevitable march to the nomination for Romney hit some major roadblocks.
In 2008, Romney won Minnesota, Colorado and Missouri, the three states that voted after Nevada, but this year Santorum swept all three, snatching the momentum from Romney and raising serious questions about the former Massachusetts governor's ability to excite his party's base.
For Santorum, he will bring that momentum into the debate, as well as the confidence that comes from recent polls showing him locked in a tight race with Romney in Arizona and Michigan. The former Pennsylvania senator, though, is likely to face questions at the CNN debate about a speech he gave in 2008 at Ave Maria University in Florida when he said Satan is targeting the United States.
"This is not a political war at all. This is not a cultural war at all. This is a spiritual war," Santorum said. "And the Father of Lies has his sights on what you would think the Father of Lies - Satan - would have his sights on: a good, decent, powerful, influential country: the United States of America. If you were Satan, who would you attack in this day and age? There is no one else to go after other than the United States."
Asked about the comments Tuesday evening after an event in Phoenix, Santorum said "these are questions that are not relevant to what is being discussed in America today." But the controversy over his remarks has the potential to derail Santorum's momentum before of next week's voting.
In a state where around 18 percent of eligible voters are Latino, according to the Pew Hispanic Center, the candidates are also likely to face questions about immigration at the Arizona debate. In 2010 ,the state's Republican Gov. Jan Brewer enacted a strict new law that ordered immigrants to carry their registration documents at all times and mandated that police question them about whether there was reason to suspect that they were in the country illegally. In the ensuing governor's race, seen as a referendum on the law, 71 percent of Latinos backed Brewer's Democratic opponent Terry Goddard, but Brewer still emerged victorious.
Romney has outlined an immigration policy that relies on "self-deportation," a policy predicated on the notion that illegal immigrants, without the ability to find employment, will voluntarily leave the country. Romney has also stated that as president he would veto the DREAM Act, the Democrats' bill to provide a path to citizenship for some children of undocumented immigrants who attend college or serve in the military, a stance that has alienated some Latinos.
The latest polls out of Arizona show Romney establishing a comfortable lead there: a new NBC/Marist poll had Romney up 43 percent to 27 percent over Santorum. But Michigan was far closer, with the poll revealing a slim 37 percent to 35 percent lead for Romney. Neither Gingrich nor Ron Paul are making a push to win in Arizona or Michigan. A new Quinnipiac poll, however, put Santorum ahead of Romney nationally: 35 percent to 26 percent. But one of the reasons cited by some pundits as an explanation for the " bubble primary " - candidates surging and plunging in rapid succession - is the huge number of debates and the effect they have on voters.
That makes tonight's duel in Mesa that much more important, especially with so much at stake next week. In addition, tonight's is the final debate before a flurry of states votes on Super Tuesday. CNN cancelled a March 1 debate in Georgia after Romney and Paul both announced they would not attend it.
The next debate is set for March 19 in Portland, Ore., but, with such an unpredictable primary, just about the only safe prediction is that the GOP race will look very different by then.
Matthew Jaffe is covering the 2012 campaign for ABC News and Univision.