Barack Obama and John Edwards try to paint her as a candidate of the Washington establishment and beholden to special interests. Chris Dodd questioned the former first lady's competence on health care reform. They have hinted she's too divisive to govern effectively as president.

The shift in tone was perhaps inevitable, coming nine months into a largely cordial primary campaign that has left the New York senator the undisputed front-runner for the Democratic nomination. In criticizing Clinton, they acknowledge she's a formidable candidate and accept that she's unlikely to stumble badly to give others an opening.

"Her opponents are starting to worry that she is consolidating her position, and that's potentially fatal for them," said Raphael Sonenshein, a political science professor at California State University, Fullerton. "A lot of people watching her campaign are surprised by the fact that it's strengthening and could be starting to break away."

The new dynamic is also a clear expression of frustration by Clinton's rivals, who were forced to the sidelines this week when she released her new health care plan. The rollout drew extensive media coverage.

Republicans are criticizing Clinton as though she's already the Democratic nominee. Rudy Giuliani has relied on newspaper and Web ads to assail her on the Iraq war.

To remain in the game, Democrats are starting to point out Clinton's potential vulnerabilities and question her electability.

At a seniors' forum in Iowa on Thursday, rival Joe Biden suggested congressional Republicans would refuse to work with Clinton to accomplish health care reform.

"Let's be frank about this," Biden said. "What's changed to make you think Hillary is going to be able to put together the 15 percent of Republicans" who will be needed to enact any overhaul of the health care system?

In an interview with The Associated Press, Dodd said Clinton had mismanaged her effort to reshape the nation's health care system during her husband's presidency and questioned why she touted that experience as evidence she should be allowed to try again.

Biden and Dodd are both polling in single digits and have had little impact on the overall dynamic of the field. But their criticisms come amid new efforts by Clinton's lead rivals, Obama and Edwards, to portray her as part of the status quo.

Edwards has been particularly aggressive, claiming Clinton lifted his health care plan and criticizing her ties to lobbyists and other special interests.

His top campaign strategist, Joe Trippi, even sent an e-mail to supporters this week blasting her for attending a fundraising lunch with lobbyists. Clinton, he wrote, is the "poster child" for what's wrong in Washington.