This leaves two scenarios, reflecting the two-man race we now see in the polls: Either Mitt Romney secures his frontrunner status with wins in Iowa and New Hampshire and goes on to win South Carolina, or a "moderately electable" Newt Gingrich wins Iowa and goes to South Carolina to break the tie (after Romney wins New Hampshire).
The following is the race as it stands in the most recent South Carolina polls:
South Carolina Primary
12/04 Winthrop -- Gingrich 38, Romney 22, Perry 9,
11/28 ARG -- Gingrich 33, Romney 22,
11/28 Insider Adv -- Gingrich 38, Romney 15,
11/21 Polling Co. (R) -- Gingrich 31,
Unfortunately, unlike Iowa and New Hampshire, there has been little polling in South Carolina. Even more unfortunately, there have been no polls taken there since Cain dropped out of the race. We can assume that Gingrich will get a chunk of the departing Cain votes, but it's also possible that a Tea Partier could pick up some of the votes.
None of the pollsters listed above has a sterling reputation. But it's clear that Gingrich enjoys a substantial starting advantage over Romney. Gingrich is--for now--perceived as more conservative than Romney, and Gingrich hails from the South. More importantly, South Carolina is influenced by the winners of Iowa and New Hampshire. For the moment, Gingrich is doing better than Romney in Iowa. For Romney to win South Carolina, there must either be a tremendous crash in Gingrich's campaign, or Romney must win Iowa.
Gingrich's campaign is untested, and it could crash. One should never assume such a crash unless the candidate is perceived as highly unelectable (like Cain or Bachmann). Unless or until the race changes dramatically, it's likely that Gingrich will prevail in South Carolina.