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Will Christianity rule Republican vote in South Carolina?

20 January 2012 Last updated at 23:04 GMT

There is another key moment on Saturday in the battle between the Republicans who hope to challenge President Obama for the White House, when the state of South Carolina gets its chance to vote.

Contender Newt Gingrich is the latest to face uncomfortable questions after his ex-wife claimed he had wanted to have an open marriage.

But beyond the personalities there are also deep ideological divides, as the BBC's North America Editor Mark Mardell reports.