There’s been talk all week of a Newt Gingrich resurgence in South Carolina, with hints of one in some recent polling.  Now comes brand new data from Public Policy Polling that shows the former House speaker storming into the lead. PPP’s survey is more of a snap-shot and only covers one night (Wednesday), but it’s the strongest evidence yet of gathering momentum for Gingrich, who leads Mitt Romney by a 34-28 percent margin.

Obviously, the race is volatile, and it’s open question whether the interview with Gingrich’s second wife, Marianne, that will air on ABC tonight will derail him at the last minute. But it’s looking more and more like we’ll have a real contest on Saturday — and not the easy victory for Romney that polls a week ago were predicting.

If you think there ought to be at least some entertainment value in politics, this is a very positive development. A clean Romney victory would effectively shut the GOP race down, but if Gingrich were to pull off the upset, all hell would break loose — at least for a little while.

The reaction to Romney’s Iowa* and New Hampshire victories shows how this works. Neither result was actually that impressive. The initial count in Iowa gave him an eight-vote edge with a lower share of the vote than he received in 2008 — and, in fact, the lowest-ever share for a caucus winner. And in New Hampshire, which is practically Romney’s home state, the  GOP electorate was ideologically and culturally ill-suited to Gingrich and Rick Santorum, leaving Romney to vie mainly with Jon Huntsman and Ron Paul. His victory was about as remarkable as Michael Dukakis’ in the state’s 1988 Democratic primary.

But because they were the only two contests to take place, the political world was left to rely on Iowa and New Hampshire as the main gauges of how the GOP race was progressing. Thus, enormous attention was paid to the fact that Romney had become the first Republican to win* both lead-off states. No one else, besides the easily dismissed Paul, seemed to do well in both states. As a result, the hype from two rather unsurprising outcomes changed the perception of Romney from “weakest front-runner ever” to “unstoppable force who’s about to run the table.” His poll numbers in South Carolina and Florida, the next two battlegrounds surged, and his national support pushed well past the 25 percent ceiling he’d faced for all of 2011. This is why he’s in position to score what would amount to a knock-out blow on Saturday; if two unimpressive wins helped him so much, imagine what a victory in a state that seems so hostile to him would do?

The flip-side to all of this, though, is that a Romney loss in South Carolina would be blown up by the media and political world just as much as — if not more than — a Romney win. Let’s say Gingrich’s momentum holds and he ends up winning by five points on Saturday. Suddenly, we’d hear all about how Gingrich has learned to hit back and run a real campaign and how he’s found a message that resonates with the conservative base. We’d also hear about how Romney’s problems with the GOP base are more real than ever and how there’s something about him that’s keeping the GOP from embracing him. And the Iowa results, which now put Santorum in first place, would be revisited. The takeaway from the first three contests would be: Romney went one-for-three, with his only victory coming in what is essentially his home state.

In this atmosphere, the Florida polling that now shows Romney crushing Gingrich would tighten dramatically. (Remember that in early December, when he was surging everywhere, Gingrich was the one with a commanding Florida lead; that’s how volatile these numbers can be.) This would set up a frantic ten-day campaign in Florida (which votes on January 31) that the media would likely portray as a referendum on Romney’s viability. There would probably be, as John Heilemann suggested on MSNBC earlier today, talk of party leaders lining up a consensus back-up candidate in the event of a second straight Romney loss (because Newt would still not be an acceptable option for most of them).

We’ve actually seen something like this before, on the Democratic side in 1992. Back then, Jerry Brown pulled off a shocking upset of Bill Clinton in the March 24 Connecticut primary, just a week after Clinton had seemingly put the nomination away with wins in Illinois and Michigan. Overnight, the narrative changed: Were Democrats getting cold feet about nominating the scandal-plagued Arkansas? This set up a heated and wildly entertaining two-week campaign in New York. If Clinton couldn’t win there, the talk went, his campaign would melt down and Democrats would recruit a white knight into the race — maybe Mario Cuomo, or Bill Bradley, or Jay Rockefeller, or someone else. Paul Tsongas, who had suspended his own campaign after Illinois and Michigan, all but announced that he’d re-enter if Clinton lost New York — and Newsday promptly endorsed him. While Brown had a chance to win New York, he was still dismissed as a serious prospect for the nomination — like with Newt, there was lots of resistance from party leaders with long memories.

The New York battle, which included a moderator-less debate between Brown and Clinton on Phil Donahue’s show, ended with a solid Clinton win. Brown may have miscalculated by announcing that Jesse Jackson would be his running-mate, a move that reopened the racial and ethnic wounds of the state’s 1988 primary, and ended up finishing behind Tsongas. The result cemented Clinton’s inevitability, and from that point on the Democratic race was a snore.

Note: Jonathan Bernstein, who wrote a prescient post on January 3 about the Newt/Jerry Brown parallel, deserves credit for inspiring this post.