MARSHALLTOWN, Iowa -- On a frigid night last week, speaking to a small crowd in a high school library here, John Edwards recalled a drive through another small Iowa town with his wife, Elizabeth.

As their van stopped at a crossroads in Ottumwa, he said, she turned to him and said, "I swear, if someone knocked on this window and asked me for directions, I could give them."

The Edwards family knows Iowa well. After two campaigns in which he's appeared at least once in each of its 99 counties, Iowa knows him well, too. And a little more than two weeks from today, no major candidate will have a bigger stake in the decisions of its Democratic voters than John Edwards.

If he wins, the momentum would make him a suddenly formidable contender for his party's nomination. If he loses, it would be hard to see how his second bid for the presidency could survive.

A loss here would be damaging to either of the other front-running Democrats as well. But with much more money and national campaign infrastructures already in place, either New York Sen. Hillary Rodham Clinton or Illinois Sen. Barack Obama could press on at least through New Hampshire, South Carolina and the quasi-national primaries clustered on Feb. 5.

Months ago, Mr. Edwards lost the polling lead he had maintained here through the first half of the year. In recent surveys, he has consistently run behind though not out of reach of Mrs. Clinton and Mr. Obama. But Mr. Edwards' partisans, as well as officials of rival campaigns, are not counting the former North Carolina senator out.

The Edwards campaign contends that it has a depth of committed supporters that has the potential to propel him past his better-funded rivals. Even if he pulls off that upset, however, a challenge looms in transforming success in the retail politics of Iowa into a national campaign.

To take the first step, Mr. Edwards is counting on people like John R. Campbell Jr., who will be caucusing in Precinct 56 in Polk County. Mr. Campbell, a lobbyist for the United Steelworkers, started the year behind former Iowa Gov. Tom Vilsack. The day that Mr. Vilsack abandoned his short-lived campaign for the democratic nomination, Mr. Campbell received a phone call from Mr. Edwards, who quickly recruited him to his grass-roots effort.

Mr. Campbell, an African-American, has deep roots in the Des Moines community. Four years ago, when he was supporting the unsuccessful candidacy of former Missouri Rep. Richard Gephardt, his caucus met in the same church in which he'd been married.

Sitting in his neighborhood coffee shop one morning last week, he said backing Edwards was an easy decision to make, given the working-class issues that form the core of the Edwards message.

"He comes from a working-class background,'' Mr. Campbell said of the millionaire lawyer, whose father worked in a North Carolina textile mill. The USW activist says he sees in his campaign a message of empowering the disenfranchised that transcends race and class.

That message was repeated on television and in person around the state last week, as Mr. Edwards made stops on a bus tour in the days before and after the final Democratic debate before the Jan. 3 caucuses. He was joined by his father and mother, and, for the first time in weeks, his wife, Elizabeth in Indianola.

Addressing the crowd, Mr. Edwards and his wife reveled in the generally positive reviews he had received for his debate performance hours earlier. He repeated the themes he had returned to throughout the Democratic contenders' last joint appearance before the Iowa voters.

"The power in our government has become concentrated in the few and the powerful," he said, as he stood before the small crowd in his campaign uniform of jeans, an open-necked shirt and a blue fleece jacket.

"Why don't we have universal health care? We don't have it because of the drug companies and the insurance companies and their lobbyists. Why do we have that mess of a prescription drug bill? Because the insurance lobbyists wrote the thing. Why do we have a bunch of lawless mercenaries running around in Iraq, working for [the] Blackwater [a private security contractor], making 10 times what our men and women in uniform make?"

It's a campaign anthem of angry populism, a cry of outrage at the influence of big drug and insurance companies, and what he describes as a Washington culture of favor-seeking corporate influence.

Gone in his stops last week and in the Des Moines Register debate Thursday were the criticisms of other candidates, particularly Mrs. Clinton, that peppered his stump speech earlier in the campaign.

Asked about the shift in tone after an appearance at a Des Moines middle school, Mr. Edwards said that in the final days before the caucuses, he planned to emphasize his own positive vision -- a repeat of the upbeat approach that came close to winning here four years ago.

Joe Trippi, a senior Edwards strategist, felt no similar constraints in the post-debate crowd Thursday, as he ticked off the reasons why his candidate could still pull through. Noting that neither Mrs. Clinton nor Mr. Obama had been able to establish a clear advantage over their rivals, he said, "There's a reason she hasn't run away with this; there's a reason why he hasn't been able to run away from her.''

He argued that the New York senator's campaign was burdened by the partisan legacy of the Clinton administration, and that Mr. Obama faced a headwind of concern over whether he had enough experience to be president. Both factors, he said, would end up helping his candidate.

The Edwards camp also hopes to be a beneficiary of reactions against the increasingly rancorous sniping between the Clinton and Obama camps. That acidic turn in the race was exemplified last week by the controversy over a since-resigned Clinton adviser's observation that Mr. Obama's acknowledgement of youthful drug use would make him vulnerable to Republican attacks.

The analogy that Edwards partisans cite hopefully is the 2004 caucus race. Weeks of bitter cut-and-thrust between the seeming leaders -- Mr. Gephardt and former Vermont Gov. Howard Dean -- seemed to have had a mutually destructive effect that created an opening for Massachusetts Sen. John F. Kerry, who won in Iowa after trailing in the polls for most of the year. Mr. Edwards also made his way through that opening, with the late charge that left him a close second.

"This time, I go into the last three weeks with a lot of strength," Mr. Edwards said last week, comparing the dynamics of the two contests. "Last time, I had to come out of nowhere. This time, Iowa caucus-goers trust me."

David Axelrod, a senior strategist for Mr. Obama, rejects the Dean-Gephardt analogy, insisting that, in contrast to 2004, only one candidate was to blame for injecting a harsher tone into the campaign's recent weeks.

"This is the sound of one hand clapping," he said. "We're not the campaign digging through kindergarten records, we're not digging into anyone's past life. I don't think that anyone perceives us as running a negative campaign."

And at least some Iowa voters find Mr. Edwards' us-against-them rhetoric too abrasive.

"He's a little divisive," said Marshalltown resident Don Benbow, as Mr. Edwards shook hands and signed autographs a few feet away in the Marshalltown High School library. "You see that corporate lawyer thing coming through." (Actually, Mr. Edwards was a plaintiffs' lawyer, not a corporate attorney.)

"I'm leaning toward Obama; he's more electable," Mr. Benbow said.

His Marshalltown neighbor, Donn Anderson, had the opposite reaction: "I'm kind of leaning in that [Edwards'] direction," he said when asked if he supported the former senator. "I kind of agree with that 'two Americas' stuff."

Mr. Anderson is a veteran of past caucuses, and the Edwards campaign contends that such supporters -- familiar with the arcane rules of the state's caucus process -- are a particular strength of their effort, which even rivals concede is among the best organized in the big Iowa field.

"We feel like we've got the kind of people that, when they get to a caucus, they know what to do," Mr. Trippi said.

One of the most important assets for caucus supporters of any leading candidate is to be able to persuade partisans of other, trailing candidates to switch to their camp during the caucuses. The Democratic rules dictate that if a candidate's supporters in a precinct do not add up to a threshold number (which varies with the district's size), their candidate is not viable. Along with the undecided participants, they make a pool of voters that the leading campaigns will vie to attract on the evening of Jan 3.

"Any member that I have that may support another candidate, their second choice is John Edwards," said Chuck Rocha, the youthful USW political director. The union has endorsed Mr. Edwards.

Anticipating the caucus-night bargaining, organizers such as Mr. Campbell have held training sessions with would-be caucus-goers. "All of the well-organized campaigns are having training sessions," he said.

Mr. Rocha and the USW, along with most other industrial unions, backed Mr. Gephardt four years ago. Other large unions, notably the Service Employees International and AFSCME, the state's largest union, backed Mr. Dean.

The union movement is split here again this year. Among the other major union players, AFSCME is behind Mrs. Clinton, and key United Auto Workers locals are working for Mr. Obama. Still, Mr. Rocha sees a better result for his candidate this year than the one he backed in 2004.

Pointing to the ceaseless campaigning and organizational work that Mr. Edward has devoted to the state since then, he said, "The difference is that John has a bigger base of support that Dick did, because John has lived here for four years."

Mr. Rocha said the USW was targeting veteran caucus-goers and contacting a second tier of voters who regularly show up at primary and general elections. The focus on regular voters represents a tactical contrast between the Edwards and Obama campaigns. While all the candidates covet support from caucus veterans, Mr. Obama's campaign is pinning part of its hopes on an effort to expand the universe of caucus-goers by reaching out to first-time participants, such as students.

"If it's snowing, it helps John," Mr. Rocha predicted.

But even if the Edwards campaign pulls off a come-from-behind victory, would that provide enough media and financial momentum to allow it to compete in the mega-state competition of the ensuing month?

"Kerry proved that [an Iowa win] opens up purse strings to all the big states," Mr. Rocha said. "All the big donors will move their money to John Edwards."

Mr. Trippi contended that momentum and media attention will increasingly trump money as the Feb. 5 mega-primary approaches. "By that stage, there's never been a case where substantial spending did anyone any good," he asserted.

Meanwhile, the Edwards bus rolls from town to town across the frigid plains.

"Here's what I believe,'' the ever-optimistic Mr. Edwards tells his audiences. "I believe we're going to have an election, not an auction, in Iowa."