MASON CITY, Iowa - Politicians keep looking for signs of erosion in John Edwards' make-or-break campaign to win the Iowa caucuses.

And not finding any - at least not so far.

Despite the widespread view that the national Democratic race for president has become a two-candidate affair, number three keeps hanging on out here in the Midwest.

Poll after poll shows the former North Carolina senator with the support of more than 20 percent of Iowa prospective caucusgoers, very much within range of Sens. Hillary Rodham Clinton and Barack Obama, and well ahead of everyone else.

"He has the goodness of the common people at heart," said Sonny Blanchard, 70, who backed Edwards in the caucuses in 2004 and plans to do so again Jan. 3. "We're not big-money people in Iowa, and every time we turn around, somebody moves a factory to Mexico."

And the candidate, who embarks today on an eight-day, 20-stop tour across Iowa on a bus dubbed the "Main Street Express," is positioning himself to be the beneficiary should the Clinton-Obama sniping heat up in a way that offends Iowa Democrats.

For the most part, Edwards has stopped taking shots at his rivals, and he has toned down his rhetoric a little.

In the last week or two, he has sounded less like the angry man of most of 2007 - outraged by the plight of the poor, the hungry and the uninsured - and more like the upbeat optimist who came from nowhere in 2004 caucuses to finish second in the caucuses behind Sen. John Kerry, the eventual nominee, with 32 percent of the vote.

On a recent icy night, Edwards gave the 150 people who came out to hear him at the high school library here a taste of the message that seems to be resonating with many Iowans.

He blamed the nation's failure to adopt universal health care on the big drug and insurance companies, its failure to address global warming on the big oil and power providers.

"Do you really believe we're going to see big change if we trade a crowd of corporate Republicans for a crowd of corporate Democrats?" he asked. "It's a big lie."

Edwards tells his listeners that the challenges facing the nation are great but that he has faith in its ability to meet them.

Why does Edwards remain a factor in Iowa even as his campaign seems to be stalled elsewhere?

One reason is familiarity; Iowans liked him four years ago, and they like him now. In a recent poll by the Des Moines Register, 86 percent of likely Democrat caucusgoers said they had a favorable opinion of him.

Another is the sheer amount of work he has put in; Edwards was the first candidate this time around to visit all 99 Iowa counties.

He has the backing of a number of several influential labor unions; the local head of the Steelworkers introduced him in Mason City.

And his call for trying to break corporate lobbyists' hold in Washington has found an audience among farmers and working people who live 1,000 miles from the capital.

Said Mark Kornblau, an Edwards spokesman: "Iowa Democrats have had the chance to see John Edwards and hear his message of standing up on behalf of regular people. They're connecting with him."

Former Gov. Tom Vilsack, who is supporting Clinton, said he was not surprised by Edwards' current standing in Iowa. "He has his organization, and he has relationships with people from last time - those things matter in the caucuses," Vilsack said. "He has what he has. His challenge is to make it grow."

As indicated by the difference between Edwards' 2004 vote and his current poll numbers, not everyone who backed him then is backing him now. In fact, some say they barely recognize him.

"This time he seems more driven, more hard-edged, less moderate," said Dennis Parrott, 52, of Newton, Iowa, a county auditor who is now backing Obama. "Now, he's a little too far left for me. I'm interested in the poor. But the middle class pays the taxes."

As Edwards soldiers on, he rejects the notion that the outcome of the first-in-the-nation caucuses is any more important for him than for the other Democrats seeking the prize.

But analysts say it is hard to see how he can force his way into the national picture without an Iowa win or something very close to it.

"I've been through this," Edwards said in Mason City. "Somebody will come out of Iowa with a lot of momentum. And somebody won't."

Contact senior writer Larry Eichel at 215-854-2415 or leichel@phillynews.com.