DES MOINES — Embracing the legacy of a grandfather who “worked the graveyard shift… in the mills,” quoting Democratic icons Franklin Roosevelt and Harry Truman and recounting the story of a teenage girl who died after being denied health care, John Edwards closed what has become a fiercely-populist Iowa caucus campaign with a roaring condemnation of war profiteering in Iraq and corporate abuse at home.

Sounding themes rarely heard from major candidates of either party in recent decades, the former senator from North Carolina attacked “the glorification of corporate profit” that would leave “children living on the streets and in cars while CEOs make billions and billions of dollars.”

“This is insanity, and it must stop!” shouted Edwards in a speech that attacked by name Blackwater, Halliburton, Exxon-Mobil and other corporations. And the crowd of steelworkers, carpenters, nurses and family farmers — one of the largest assembled for any candidate during the course of the campaign leading up to Thursday’s caucuses — responded with wild applause for Edwards’ promise to break “the iron grip” of corporate power.

The crowd at the Edwards event numbered more than 3,000, roughly twice that assembled at Des Moines-area rallies Wednesday night for Illinois Senator Barack Obama and New York Senator Hillary Clinton.

Of course, Edwards had help. Singer John Mellencamp joined the candidate on stage at the Val Air Ballroom in West Des Moines. The popular performer, who helped to organize the Farm Aid concerts, drew plenty of wavering voters to the event.

Whether Edwards reached those sympathetic-but-uncertain voters will decide the fate of a campaign that will have a difficult time moving forward without an Iowa win.

There is little question now that Edwards and Obama are competing with one another for the votes of Iowans who want to nominate an agent of change. This week’s Des Moines Register survey of likely Democratic caucus goers found that voters were more interested, by a 2-1 margin, in selecting a candidate who would shift the direction of the nation than in choosing one who merely offers the promise of sound leadership.

Clinton’s got the clear advantage among those who are most interested in leadership skills. And she could still win with their support.

But Edwards and Obama are grabbing for the “change” mantle that each man believes has the potential to vault him into position to displace Clinton as the national front-runner.

Edwards and Obama are going at it from decidedly different directions, however. Since emerging as the leader in surveys of likely caucus-goers, Obama has waged a relatively soft and safe, “can’t-we-all-just-get-along” campaign — going so far as to air television and radio ads celebrating the appeal of his centrist themes to Republicans who his campaign specifically urges to caucus on his behalf. (In Iowa, anyone who shows up at a party caucus can participate.)

Obama’s still ahead in most Iowa polls. But, as Edwards has surged in recent weeks, the Illinoisan has picked up some of his rival’s populist langauge. One of Obama’s last television ads has the senator declaring that, “I’ve spent my life working for change that’s made a real difference in the lives of real people. That’s why I passed up a job on Wall Street to fight joblessness and poverty on the streets of Chicago when the local steel plant closed. That’s why I turned down the corporate law firms to work as a civil rights lawyer, to fight for those who’ve been denied opportunity.”

But even in his “populist” commercial, Obama features “I brought Democrats and Republicans together” themes.

No one should doubt the power of Obama’s unity appeal. He delivers it well. And, after the divisiveness of the Bush-Cheney years, there is indeed something refreshing about the prospect of a president who embraces the promise of negotiation and compromise.

“Change isn’t going to come because people are hollering more, talking tough… We don’t need more heat. We need more light,” says Obama, clearly seeking to contrast his message with that of Edwards.

Edwards begs to differ.

He is not looking for the middle ground at this point. He’s not promising “win-win” solutions.

“I don’t believe you can sit at a table and negotiate with drug companies, insurance companies and oil companies and hope that they will voluntarily give their power away,” the 2004 Democratic vice presidential nominee explained in Des Moines Wednesday night. “They will give their power away when we take their power away.”

Though he did not mention Obama by name, it was pretty clear that Edwards was speaking of his more soft-spoken rival when he declared “the status quo and good intentions are not enough.”

“Corporate greed is robbing our children of the promise of America. It is time for us to fight back,” shouted Edwards to the cheering crowd at the Val Air ballroom. “You better know that tomorrow night you need to send a fighter and a warrior into that battle on your behalf.”

What Edwards knows is that — while Obama can afford to run second and perhaps even third in Iowa — the option is not available to him. Without an Iowa win, Edwards does not have the money or the poll numbers to renew his candidacy in the New Hampshire primary that comes barely 100 hours after the caucuses finish.

So Edwards is telling Iowa Democrats that Thursday is the populist make-or-break moment. And he is promising them an epic shift in the political process if they embrace it.

“What will happen when you are finished is that you will start a tidal wave of change that will sweep across this country with a power that cannot be changed, that cannot be stopped,” says Edwards.

Actually, what will happen depends on what Iowans decide in a matter of hours. They want change. But they have yet to define the sort of change they want. That will happen Thursday night, when caucus goers choose between the soft promise of Barack Obama and the edgier populism of John Edwards. Or when they divide closely enough between the two to give a win, and the momentum that goes with it, to the woman who until a few months ago was supposed to have this thing all wrapped up.