John Edwards (search), his campaign boosted by criticism of U.S. trade policy and the loss of jobs to overseas markets, on Thursday called trade "a moral issue" that sets him apart from John Kerry (search) in the race for the Democratic nomination.

"When we talk about trade, we are talking about values," Edwards said in a speech at Columbia University as he tried to build on a surprisingly strong second-place showing in the Wisconsin primary.

The North Carolina senator focused on the economy and jobs while campaigning in Wisconsin, largely by making the case that trade agreements like the North American Free Trade Agreement (search) have led to a flow of high-paying jobs to China and other low-wage countries.

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Edwards said he believes the same theme will work in the 10 states holding "Super Tuesday" primaries March 2. He is targeting Georgia, Ohio and the industrial regions of upstate New York.

While Kerry has been critical of the way free-trade deals have been carried out, the Massachusetts senator voted for them, setting the stage for the loss of jobs in the United States, Edwards said.

"There is no question that our current trade policies are good for the profits of multinational corporations," he said. "They are good for some people in the financial sector here in New York City -- not all, but some."

Edwards walks a fine line between waging an upbeat and positive campaign -- a pledge for which he has gained voter support -- while pointing out differences with Kerry.

"When it comes to bad trade agreements, I know what they do to people," he said. "I have seen it with my own eyes what happens when the mill shuts down."

Edwards later challenged Kerry to debate him in Georgia, a state he is targeting. "It would be a real loss for our party if Senator John Kerry and Senator John Edwards didn't debate right here in the state of Georgia," he said at an Atlanta rally.

Edwards and Kerry already have agreed to debate once in California. Talks are ongoing about other debates.

Edwards said his second-place showing in Wisconsin has given him the steam to push through the 10-state primary on March 2, and beyond to tests in Texas and Florida on March 9.

Edwards, whose father worked at a mill in North Carolina, said he has a better understanding than Kerry of blue-collar issues. He told his college audience Thursday that his disagreements with Kerry extended well beyond NAFTA and include many trade agreements he has opposed.

"Those trade deals were wrong," he said. "They cost us too many jobs and lowered our standards."

As he pushed forward into the March 2 round of voting, Edwards was forced to set aside precious campaign time to raise money. He attended a fund-raising event in New York and was heading to Florida on Thursday for another.

The difficulties Edwards faces in exploiting the trade issue were underscored Thursday when the AFL-CIO endorsed Kerry, a signal that key segments of the party establishment think the nomination fight is essentially over.

Edwards said that while union leaders may be coalescing behind Kerry, he is winning the battle for rank-and-file members who face the daily pressures of jobs losses.

"I've done extraordinarily well among union households," he said. "If you look at what's happened in the early primaries, I have not had the endorsement of labor unions and I've done very well. I will continue to speak directly to union households and working people."

Although Edwards said he had strong support in union households, exit polls conducted for The Associated Press showed that such voters tended to support Kerry by narrow margins in Iowa and Wisconsin and by substantial margins -- from 20 to 40 percentage points -- in Missouri and Delaware.

The exit polls were conducted for the AP and television networks by Edison Media Research and Mitofsky International.