It's down to a four-way contest in Iowa, the closest since 1988, focused on the growing number of undecided voters suddenly choosing sides.
Polls in the state suggest all four are competing for the lead within the error margins. Here are the latest polls:
"Any one of those four could win," said pollster Del Ali of Research 2000, who conducted the poll for KCCI-TV of Des Moines. "The biggest surge without question is Edwards. Both Kerry and Edwards have momentum."
Sens. John Kerry of Massachusetts and John Edwards of North Carolina were drawing the most support from the last-minute shoppers, campaign pollsters and strategists said. After starting the week behind Dean and Gephardt, the two senators closed the gap in a race that is impossible to predict because the vagaries of the caucus system makes polling unreliable.
The stakes are highest for Gephardt, who won the 1988 caucuses by four percentage points — a landslide in comparison to where the race stood Friday. A defeat would effectively end the Missouri lawmaker's 28-year political career, aides said.
"I've always known this would be a close competition, a dead heat-type race, but I believe we're going to win," Gephardt told supporters in Fort Dodge in northern Iowa.
Public polls showed his support slipping, and trouble signs loomed in internal campaign surveys. An official close to Dean's advisers, speaking on condition of anonymity, said their research showed Kerry leading, followed by Dean and Edwards — all within the margin of error — and Gephardt narrowly trailing.
CBS News Correspondent Bob Schieffer, a 25-year veteran of political campaigns, says it's too close to call
"I don't think there's any question Dean has slipped a bit here,'' Schieffer said. "I think this race is up for grabs."
Those numbers don't bode well for Dean, but others statistics do: 3,500 volunteers knocking on doors, more than three times his closest rival, and about $300,000 raised from Internet-savvy supporters Friday, three times as much as any other day this week.
"We're surging because our supporters believe our rivals are not just trying to stop Dean, they're trying to stop them," said spokeswoman Tricia Enright. Dean's supporters have a history of responding when his back is against the wall.
The former Vermont governor has the money and organization to compete well beyond Iowa regardless of Monday's results, but a defeat would strip him of the front-runner status, raise questions about his long-term viability and embolden his rivals.
Chief among them Kerry, whose campaign was at death's door when the year began. He lost a big lead to Dean in New Hampshire months ago and, in a last gasp, shifted his resources to this caucus state.
A strong finish or victory in Iowa might resuscitate Kerry's campaign in New Hampshire. From nearby Massachusetts, the senator has served 35 years in public life after a medal-winning tour of duty in the Vietnam War.
"What I've done tells you something about the risks I'm willing to take, about my character, about my priorities," Kerry said in Decorah, Iowa, where he tried to recruit undecided voters. He won some converts after stripping off his coat and playing quarterback in a pickup football game with college students.
"It shows he's ready to get dirty," said Luther College sophomore Marc Kalin.
But, for now, Kerry and Edwards stuck to their positive political messages. Edwards, in an interview with The Associated Press, called on Dean, Gephardt and Kerry "to also stop their negative mail."
No campaign swore off negative radio or mail ads, and a Dean spokeswoman criticized Kerry for suggesting eight years ago that the Agriculture Department should be eliminated. Kerry's campaign called it a typically negative attack from Dean.
Despite the dose of acrimony, Dean and Gephardt opted to close with upbeat television.
Dean stopped broadcasting an ad that singled out his three opponents as "Washington Democrats" who backed the Iraq war. Gephardt responded by asking television stations to stop airing an ad that criticizes Dean's record on Medicare and Social Security.
"The only reason our spot was ever on the air was because he attacked Dick Gephardt," said Gephardt campaign manager Steve Murphy.
Each of the four campaigns hope to gain momentum for New Hampshire's Jan. 27 primary. Wesley Clark, who skipped Iowa to focus on shaving Dean's lead in the Granite State, took a slap at the front-runner from afar.
Releasing his financial and other personal records, Clark said, "Everybody ought to be open about what they've done in public life." Many of Dean's official records as governor of Vermont are being kept secret.
New Hampshire Democratic Party chairwoman Kathleen Sullivan said a surprisingly large number of voters are still undecided, with many awaiting results from Iowa.
"It's as tight as a tick," she said.
Sen. Joe Lieberman of Connecticut, who also bypassed Iowa for New Hampshire, lags in polls but said a muddled result Monday night would help him. "The bottom line is this is an open, Democratic contest, totally undecided," he said.
Dean traveled to smaller towns in northern Iowa on Friday, giving an abbreviated stump speech without taking questions as he normally does. Although he portrayed his rivals as entrenched Beltway politicians tied to the special interests, he did not single out his opponents by name as he had in recent days.
"All the other folks are fine folks. If one of them wins, I'm going to support them. But they aren't going to change America and America needs to be changed," he said.