Democrats in Iowa will cast the first votes of the 2004 presidential race in the early hours of this morning (Irish time), with polls showing Mr John Kerry holds a surprise lead in the tight four-way contest.
Mr Kerry, Mr Howard Dean, Mr Richard Gephardt and Mr John Edwards are all within striking distance of victory in what could be the closest race in the history of Iowa's caucuses, the first major step in choosing a Democratic challenger to President Bush in November.
A Reuters/MSNBC/Zogby poll today shows Mr Kerry expanding his slim lead over Mr Dean to 3 points, pulling ahead 25 per cent to 22 per cent. Mr Edwards moved into third place at 21 per cent and Gephardt fourth at 18 per cent.
At least 100,000 Democrats are expected to brave sub-freezing temperatures tonight to attend one of nearly 2,000 local precinct caucuses around the state.
A loss for Mr Dean, the long-time front-runner who has scored a series of big endorsements in recent weeks, would open the door for other candidates and turn what was shaping up to be a quick Dean victory into a dogfight.
The former Vermont governor declared himself "ripping, roaring and ready to go" and shrugged off his drop in the polls.
"If we win tonight, it's going to be very difficult to stop us - the ultimate comeback kid - and then we will have gotten all this stuff behind us," he said.
A win for Mr Kerry, a senator from Massachusetts, would be a huge boost to what had been a struggling campaign. But Mr Gephardt, the congressman from neighboring Missouri and one-time leader in Iowa polls, has the most to lose.
His campaign could be over with a loss in the state.
"I always knew it would be a tight race, Iowans are tough judges," Mr Gephardt said. At a rally for union workers outside the state capital Des Moines, he urged them to "go to every house" and bring out supporters.
Mr Kerry and Mr Edwards, a first-term senator from North Carolina, surged as voters took a fresh look at the candidates after the holidays and responding negatively to an exchange of harsh attack on Mr Dean and Mr Gephardt.
Mr Dean is not only under siege in Iowa but has seen his once huge lead in New Hampshire falter under the advance of retired general Wesley Clark, who is not competing in Iowa.