| COLUMBIA, South Carolina
COLUMBIA, South Carolina Republicans John McCain and Mike Huckabee are in a statistical dead heat as voters head to the polls in South Carolina's presidential primary, according to a Reuters/C-SPAN/Zogby poll released on Saturday.
Huckabee, a former Arkansas governor, shaved six points off McCain's lead in the tracking poll to trail the Arizona senator by just one point, 27 percent to 26 percent, as voting began -- well within the 3.4 percent margin of error.
In Nevada, which also holds a presidential nominating contest on Saturday, Democrat Hillary Clinton maintained a stable 6-point lead over rival Barack Obama, 45 percent to 39 percent, with John Edwards well back at 6 percent.
In both states, large pools of undecided or persuadable voters make the outcomes unpredictable. The uncertainty is compounded in Nevada, a relative newcomer to early nominating contests, because it has no real track record on turnout.
"It's a very close race in Nevada -- it's all about turnout," said pollster John Zogby. "It's probably Clinton's to lose, but how engaged will people be to come out and vote?"
Huckabee, a Baptist minister whose January 3 win in Iowa was fueled by support from evangelicals, has pulled even with McCain in South Carolina by gaining ground among Republicans and conservatives.
McCain still holds healthy leads among independents and Democrats, who do not hold their primary in South Carolina until next Saturday.
"It was a good day for Huckabee, he caught McCain among Republicans," Zogby said. "The key for McCain is going to be how many Democrats turn out for him here."
South Carolina and Nevada are the next battlegrounds in a chaotic race to choose candidates for November's election to succeed President George W. Bush, and so far no one in either party has been able to claim the role of favorite.
The first five major contests produced five different winners. Saturday's contests will give several top contenders a chance to win consecutive contests for the first time.
About 7 percent of Republican voters in South Carolina were unsure who they would support, and about 6 percent of Democrats in Nevada uncertain. Nearly one of every five Republican voters in South Carolina who back top contenders said they could still change their minds.
OBAMA VS. CLINTON
Obama, an Illinois senator, and Clinton, a New York senator, split the first two Democratic battles and have been running close in polls in Nevada. Clinton, who would be the first woman U.S. president, led Obama among women, older voters and voters in union households. She also had double-digit advantages among white and Hispanic voters.
Obama, who would be the first black U.S. president, led by almost 3-to-1 among black voters and enjoyed a double-digit edge among younger voters.
Republicans also hold a contest in Nevada on Saturday in a race that has drawn less attention. The Republican race in Nevada was not polled by Zogby.
The Republican presidential contenders have focused instead on South Carolina, the first primary in the South. McCain, who won New Hampshire, hopes to rebound from his loss in Michigan on Tuesday.
McCain finished second there to Mitt Romney, a former Massachusetts governor who won with promises to revive the state's ailing manufacturing base and ease economic worries.
The economy was also the top concern of South Carolina voters, with 31 percent listing it first. Immigration was next at 17 percent and the Iraq war followed at 15 percent.
Romney was in third place in South Carolina with 16 percent, while former Tennessee Sen. Fred Thompson, who has staked his future in the race on a strong showing here, was at 12 percent.
Texas Rep. Ron Paul was at 4 percent and former New York Mayor Rudy Giuliani was at 3 percent.
The rolling tracking polls of 817 likely Republican voters in South Carolina and 757 likely Democratic voters in Nevada were taken Thursday and Friday. The Nevada poll had a margin of error of 3.6 percentage points.
In a rolling poll, the most recent day's results are added while the oldest day's results are dropped in order to track changing momentum.
(Editing by Todd Eastham)
(For more about the U.S. political campaign, visit Reuters "Tales from the Trail: 2008" online at blogs.reuters.com/trail08/)