Editor's note: John Avlon is a CNN contributor and senior political columnist for Newsweek and The Daily Beast. He is co-editor of the new book "Deadline Artists: America's Greatest Newspaper Columns."
(CNN) -- All presidential primaries matter, but some matter more than most.
South Carolina has voted for the eventual winner of the Republican nomination since 1980. And for the conservative candidates looking to stop the inevitability narrative that has surrounded Mitt Romney's candidacy, South Carolina is a must-win state. Here are three things to watch as South Carolinians vote.
Newt-momentum again? Newt Gingrich is a political Lazarus in the midst of his third rise from the dead here in South Carolina. After a disappointing fourth place finish in Iowa and New Hampshire, many political observers thought the former speaker of the House was finished. But his strong and substantive debate performances have helped shift the winds in his direction once again.
Earlier this week, polls started showing him closing the gap with Romney, with some even showing Gingrich pulling ahead. South Carolina is a good state for his defiantly anti-PC style and political reform message.
Opponents have once again tried to go negative on his sometimes tumultuous personal life, but it remains to be seen whether those attacks are already baked in the cake. Rick Perry getting out of the race and immediately endorsing Gingrich was a huge boost. If Newt can win South Carolina, we have a real race in front of us.
Romney downplaying expectations: Roaring out of a strong broad-based win in New Hampshire, Mitt Romney seemed unstoppable. Some pundits occupied themselves with sorting through his likely VP picks. But a week is a long time in politics, and in the course of one morning, Mitt found out he had in fact lost Iowa to Rick Santorum and fallen behind in some polls. Simultaneously, questions were raised about his self-admitted (but not completely disclosed) 15% tax rate and Cayman Islands investments.
The much-vaunted endorsement of South Carolina Gov. Nikki Haley might prove to be more of a national story than a local influence; she is currently less popular in the Palmetto State than Barack Obama.
A Thursday debate performance in which Romney tried to still play the front-runner and stay above the fray didn't help matters. But even as the Romney campaign downplayed expectations of a win -- and blanketed the state with robocalls (I received two essentially back to back, one from the Restore America super PAC and the other from Ann Romney, a total coincidence, I'm sure) -- Romney can't be counted out, even in this state. He still has the best organization of the bunch.
An evangelical bump? Rick Santorum was supposed to get a big bump when evangelical leaders gathered at a Texas ranch and announced their intention to support him.
It was historic and in a state stereotyped as an evangelical bastion, home to Bob Jones University, it was supposed to be a game changer. But so far, no game has changed: Rick Santorum remains stuck in a distant fourth place, according to the polls. There is still time for votes to shift in his direction, but this failure to materialize is a significant question mark hanging over South Carolina as its citizens prepare to vote.
The opinions expressed in this commentary are solely those of John Avlon.