South Carolina is the gateway to the White House for Republicans, as no candidate since 1980 has become the party's nominee without winning there first.
And Senator John McCain is now emerging as the man to beat after he put in a strong performance in a debate in the state on Thursday and captured the front-runner status in the latest Fox News poll.
The next test for the six Republican candidates comes on Tuesday in Michigan, where Mr McCain is locked in a tough battle against Mitt Romney.
In the debate, Mr Romney criticised Mr McCain for being less than optimistic about the state. Mr McCain said that lost manufacturing and auto industry jobs were not coming back. "I disagree," Mr Romney said. "I'm going to fight for every single job." Mr McCain replied that those voters in New Hampshire had appreciated his willingness to deliver home truths.
South Carolina, which holds its Republican primary on 19 January, is often called "the buckle of the bible belt", because of its large Christian conservative electorate, which some pundits see as playing into the hands of the Baptist pastor and former governor of Arkansas, Mike Huckabee.
But the campaign of the arch-conservative Tennessee candidate Fred Thompson stirred into life in South Carolina. He said Mr Huckabee was weak on terrorists, soft on immigration and believed in big government. "That's not the model of the Reagan coalition, that's the model of the Democratic Party," he said in one of the liveliest exchanges of the evening.
Mr McCain benefited from the debate's focus on national security, where his defence of the military plays well in South Carolina, rather than immigration, a subject on which he is seen as vulnerable.Reuse content