Following the Nevada caucuses, the political narrative was pretty well settled. Bernie Sanders' big win cemented his place as the frontrunner and the likely nominee. Biden had long counted on a South Carolina win, but his so-called firewall was looking anything but reliable. Four polls released between mid-February and the day of the Nevada caucus (February 22), showed Biden with a slim four to a five-point lead over Sanders.

But, in the wake of Nevada, we see something of a Biden bump. Polls taken post-Nevada caucuses show Biden opening a wide lead over Sanders of anywhere from seven to 20 points. For example:

  •  A Marist/NBC poll taken February 18-21 (pre-Nevada), found Biden at 27 percent with Sanders trailing by just four points at 23 percent.
  •  A Monmouth poll, taken post-Nevada (2/23-25), shows Biden at 36 percent and Sanders much farther back at 16 percent. 

Both polls estimated the African-American turnout in the 55-57 percent range. But, in the Marist, pre-Nevada poll, Biden was ahead with black voters by just 10 points. In the Monmouth poll, Biden has a much wider 28 point lead among black voters. 

Why the upswing for Biden? Perhaps South Carolina voters are pushing-back on the media's perception of an-all-but inevitable Sanders nomination (much like New Hampshire voters did in 2008 with Hillary Clinton). Or, perhaps African-American voters are 'coming home' to the candidate they know best. 

Either way, can South Carolina be Biden's "Comeback Kid" moment? And, if so, can he sustain this momentum through Super Tuesday?

To the first question — can Biden have a comeback moment — a lot of that will be determined not just by the margin of victory, but by the media interpretation of that margin. Sanders won Nevada by 26 points. Does a Biden 10-point win (in a state where, at one point, he was leading by more than 30 points), count as a breakthrough and potentially game-changing moment? 

The next question is whether Biden's momentum can help him overcome his other clear shortcomings in the Super Tuesday states.

First, Biden has been outgunned on the airwaves in Super Tuesday states. According to data compiled for the Cook Political Report by Advertising Analytics, as of February 25, in 13 of the 14 states voting on Super Tuesday, neither the Biden campaign nor Unite the Country, Biden's affiliated SuperPAC, had any TV or digital presence. The campaign has spent about $100,000 in North Carolina, but it's not clear if that was dedicated to the South Carolina primary or North Carolina's Super Tuesday primary. 

Every other major candidate in the race has put more money on-air/digital than Biden has. Even the two hastily formed SuperPACs dedicated to Amy Klobuchar (Kitchen Table Conversations), and Elizabeth Warren (Persist PAC), have spent more money ($2.13 million) on the Super Tuesday states than the one-time undisputed frontrunner and former Vice President. 

And, of course, the biggest unknown of all is whether Mike Bloomberg's $156 million in spending in these states could blunt any momentum Biden may get from a South Carolina win. Right now, according to FiveThirtyEight poll tracking, Bloomberg is at or above 15 percent threshold in some of the biggest states (California, Texas, and North Carolina), but fails to reach that same threshold in states with fewer African-American voters like Colorado, Massachusetts and Minnesota. If the story from South Carolina is that Biden has coalesced the black vote, will Bloomberg's current success with these voters fade as they move back to Biden? If so, Bloomberg would find himself picking up fewer delegates on Super Tuesday. 

But, Biden has more than just Bloomberg to worry about. Like the former New York City mayor, Biden's polling below viability in Colorado, Massachusetts and Minnesota. Biden needs a South Carolina win to help him consolidate white voters as well. 

The other big roadblock standing in the way of potential Biden momentum is the fact that so many voters have already cast their ballots. According to the Texas Tribune early vote tracker, over 425,000 ballots have been cast in the Democratic primary. In California, according to Political Data Inc., more than 1.3 million Democratic ballots have already been sent in. And, in North Carolina, the Civitas Institute tracker shows more than 205,000 Democratic votes cast. 

As we head into Saturday's vote in South Carolina, the one thing we do know is that anything but a Biden win would be a huge shock. What we don't quite know is if a Biden win will be enough to change the trajectory of this race going into the crucial Super Tuesday states. A lot of that will depend on the margin and the media's interpretation of that margin. Even so, Sanders, at this point, is likely to be the only candidate to be able to pull delegates from every one of the Super Tuesday states, meaning that Sanders will still walk away on March 3 with the largest haul of delegates. 

More from the Cook Political Report