The latest horserace polls out of South Carolina show Newt Gingrich surging in advance of Saturday’s Republican primary, with automated polls conducted Wednesday and Thursday showing Gingrich even or ahead of Mitt Romney.

Almost all of the latest surveys exclude cell phone-only voters and are conducted using controversial automated voice methods. Nevertheless, a high quality NBC News/Marist poll released Thursday showed a sharp tightening of the race following Monday’s debate. Romney led by 15 points among likely voters (37 to 22 percent) among interviews conducted the day of the debate, but by a smaller five points on Tuesday. A CNN/Time/ORC poll released Wednesday also showed a tightening in the race.

How big is the cell-phone only problem in South Carolina? Over a quarter of South Carolina adults (26 percent) were only reachable via mobile phones in data from 2009-10 (big pdf), slightly higher than the national rate at the time. The impact may be muted in a GOP primary, as cell-phone only rates are higher among racial minorities, who tend to vote Democratic.

Where is Gingrich surging?

Gingrich is up from 17 to 28 percent among men since early January, according to the CNN/Time poll. His support among tea party supporters has also edged up from 23 to 31 percent, while he continues to perform poorly among those who are neutral or opposed to the movement (13 percent in both polls).

Romney’s support has dropped by 9 points among born-again Christians since earlier this month, a group he struggled with mightily in the Iowa caucuses. It’s unclear if any one candidate has benefitted from this drop off. Born-again Christians – who made up 60 percent of primary voters in 2008 – haven’t shifted entirely to Gingrich in the CNN poll, who gained a statistically insignificant three points among evangelicals. And Rick Santorum, who won born-again Christians by a wide margin in Iowa, gained no ground among evangelical voters since early January. Automated polls currently show Gingrich with a wide lead among evangelical Christians.

Texas Rep. Ron Paul and Santorum appear to be competing for third place, each earning support in the low to mid-teens. Before he dropped out, Texas Gov. Rick Perry was winning single digit support.

Stay tuned to Behind the Numbers for what to watch for in the South Carolina primary as well as exit poll analysis on Saturday night. Have plans? Follow @Postpolls on twitter for top exit poll results in 140 characters or less.

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