John McCain, Mike Huckabee and Mitt Romney have now each won major GOP primaries, but since 1980 it's the winner South Carolina that's gone on to win the Presidency:
As the Republican presidential hopefuls focus on South Carolina, a new tracking poll shows John McCain in the lead in the state that effectively killed his 2000 campaign.
The Reuters/C-SPAN/Zogby survey gives McCain the support of 29 percent of likely voters in Saturday's crucial primary, ahead of Mike Huckabee with 23 percent and Mitt Romney with 13 percent.
The three candidates have split the first three major contests, with Huckabee winning in Iowa, McCain in New Hampshire, and Romney in Michigan.
Fred Thompson, who is making his last stand in South Carolina, was in fourth with 12 percent. Ron Paul had 6 percent and Rudy Giuliani had 5 percent in the poll, which has a margin of error of plus or minus 3.4 percentage points.
Since 1980, no Republican has won the nomination without winning the first-in-the-South primary in South Carolina.