In a raw populist appeal, Democrat John Edwards on Saturday accused presidential rival Hillary Rodham Clinton of defending a lobbyist-driven political system that is "rigged against regular Americans" and killed her plan for universal health care.

The former North Carolina senator accepted a major union endorsement while insisting that no Democratic candidate legitimately can promise to change America without swearing off special interest money from federal lobbyists. New York Sen. Clinton has refused to do so.

"When it comes to the existing lobbyist game, we've got to end it and not defend it," Edwards told more than 700 members of the United Brotherhood of Carpenters union.

The anti-lobbyist challenge is not new for Edwards. But he stepped up his attacks against Clinton by focusing on her most notable leadership role in 30 years of public life -- the health care plan that, as first lady, she drew up in 1993 for her husband, then-President Clinton.

"For more than 20 years, Democrats have talked about universal health care. In 1993, Democrats controlled both chambers in Congress" and voters had elected "a president who actually had the courage to propose a plan for universal health care. It was completely killed" by lobbyists for insurance companies and the health care industry, Edwards said.

"You don't have to take my word for it," he said. "You can ask the person who was in charge." That would be Clinton, her party's presidential front-runner.

Illinois Sen. Barack Obama, who is casting himself as the campaign's agent of change, took a similar approach late Friday night in San Francisco. Speaking to a crowd of 3,000 women, he took issue with Clinton's claim that she is the only candidate with the experience to lead effectively.

"There are those who tout their experience working the system in Washington. I understand that," Obama said. "But the problem is, the system in Washington is not working for us."

The "change versus experience" debate is the dominating narrative of the Democratic nomination fight. A Gallup Poll released this past week found that 73 percent of Democratic voters say they favor a presidential candidate who advocates changing the system, while only 26 percent opted for experience.

The poll-savvy Clinton is trying to seize both the change and experience mantle.

On a recent trip to New Hampshire, Clinton stood by her husband and said, "I've learned you bring change by working in the system established by the Constitution. You can't pretend the system doesn't exist."

Edwards replied Saturday: "Senator Clinton is right. You can't pretend the system doesn't exist. But you can't also pretend that it works."

Edwards is portraying himself as an outsider, which is hard for a former senator and vice presidential nominee to do. But he argues that only a full assault of the political system can lead to real changes on energy policy, the health care system and economic inequality.

"This election is about whether or not we're going to have real change. The change we need is not just about replacing George Bush, although, Lord knows, we need to replace George Bush. The change we need is also not just change a bunch of corporate Republicans for a bunch of corporate Democrats," he said.

To the roars of the union members, Edwards said, "Washington is rigged against regular Americans, against working Americans like you and the men and women you represent, whose interests and concerns don't stand a change against the onslaught of lobbyist in Washington, D.C."

The political implication of two candidates -- Edwards and Obama -- attacking a third on similar grounds is difficult to predict.

The criticism from both rivals could hinder Clinton's effort to be known as an accomplished agent of change. But it could split between Edwards and Obama the votes of people demanding change, buoying the establishment-driven candidacy of Clinton.

Her "experience to change" rhetoric will severely tested throughout the campaign.

First, it is no easy task to wage a change agent candidacy from the Senate, seven years removed from the White House.

Second, her rivals are starting to complain that Clinton has no right claiming to have the experience needed to lead the country, given that she never has led a government or business and that her singular policy campaign -- health care reform in 1993 -- was an unmitigated bust.

Clinton's advantages might include the fact that electing the first female president would be, in itself, a sign of great change. Also, her 30 years in public life are seen by many voters as a stand-in for experience, and a nation at war often looks to candidates who have been tested.