Democrat Barack Obama surged to a four-point lead over John Edwards in Iowa, with Hillary Clinton fading to third just hours before the first presidential nominating contest, according to a Reuters/C-SPAN/Zogby poll released on Thursday.
Obama and Edwards gained ground overnight in the tracking poll, and Clinton fell four points to third place -- a finish that, if it held, would deal a dramatic setback to the one-time Democratic front-runner.
Obama was at 31 percent among likely Democratic caucus-goers, Edwards at 27 percent and Clinton 24 percent. No other Democrat was in double digits.
In the Republican race, Mike Huckabee expanded his lead to six points, 31 to 25 percent, over former Massachusetts Gov. Mitt Romney, the one-time leader in Iowa who has attacked Huckabee for his record as Arkansas governor.
Former Tennessee Sen. Fred Thompson is in third place in the Republican race at 11 percent and Arizona Sen. John McCain slipped two points to 10 percent. Texas Rep. Ron Paul also registered 10 percent.
"There is a clear Clinton fade," pollster John Zogby said. "None of it has been dramatic, but it has been steady."
He said Clinton, a New York senator, was losing ground to Obama, an Illinois senator, among Democrats -- as opposed to independents -- and self-described liberals.
"Under any circumstance, a 31-27-24 spread is still very close," he said of the margins for the top three Democratic contenders. "Edwards is right in the mix and he has made gains too."
About 6 percent of Republicans and 5 percent of Democrats remain undecided, leaving room for late swings.
The rolling poll of 905 likely Democratic caucus-goers and 914 likely Republican caucus-goers was taken Sunday through Wednesday and has a margin of error of 3.3 percentage points for each party.
New Mexico Gov. Bill Richardson was fourth with 7 percent and Delaware Sen. Joseph Biden was at 5 percent. Connecticut Sen. Chris Dodd was at 1 percent and Ohio Rep. Dennis Kucinich was under 1 percent.
Iowa opens the process of choosing the next U.S. president on Thursday night, kicking off a state-by-state battle to choose Republican and Democratic candidates for the November election to replace President George W. Bush.
Obama, Clinton and Edwards have battled for the lead in Iowa for months. Clinton, who would be the first woman president, holds a slight lead among women and is still strong among older voters. Obama leads among men and younger voters.
Edwards, a former North Carolina senator, remained the top second choice of Democrats. A candidate must have 15 percent support in each precinct to be viable or their supporters can switch to another candidate.
In the Republican race, Huckabee gained three points on Romney. The gains followed Monday's news conference where he said he would not air an ad attacking Romney because he wanted to keep the race positive -- and then showed it to reporters.
The move was heavily criticized in the media -- but his numbers have climbed since, Zogby said.
"Everyone outside of Iowa laughed at what appeared to be a Huckabee gambit, but Iowa Republicans seem to think it was genuine," he said.
"Huckabee is not pulling away, but it's now a six-point lead and he has moved above 30 percent."
Former New York Mayor Rudy Giuliani, who has largely bypassed Iowa to focus on later voting states, is at 6 percent. California Rep. Duncan Hunter is at 1 percent.
The rolling tracking poll concludes with these results. 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 Eric Walsh)