Both those challenging her for her party's presidential nomination and the Republicans who hope to oppose her next fall pounced on what they saw as a misstep by the Democratic front-runner, portraying her as unable to give a straight answer on this and other issues.

The Clinton campaign issued a statement yesterday to The New York Times indicating that the senator supports New York Gov. Eliot Spitzer's goal of giving a special New York driver's license to illegal residents. The statement stopped short of endorsing the specifics of Spitzer's plan, which has grown more complicated as he has tried to quiet a political firestorm over the three-tiered system.

The dispute arose in the final moments of a two-hour session in Philadelphia that aired on MSNBC on Tuesday night. Prodded by moderator Tim Russert, Clinton said Spitzer's plan “makes a lot of sense. What is the governor supposed to do? He is dealing with a serious problem.”

Then she added: “Do I think this is the best thing for any governor to do? No.”

Her answer was challenged by the two candidates who had spent much of the night sharpening their attacks on the front-runner.

“Unless I missed something,” said former North Carolina Sen. John Edwards, “Sen. Clinton said two different things in the course of about two minutes.”

Illinois Sen. Barack Obama said: “I was confused on Sen. Clinton's answer. I can't tell whether she was for it or against it, and I do think that is important.”

Both candidates said they supported the plan at the debate. Yesterday, they broadened their criticism, suggesting Clinton has been vague on other topics such as Iraq, Iran and Social Security.

“It looks like they may have found a vulnerability,” said pollster John Zogby. “It's a legitimate question about her.”

The debate had featured some of the toughest attacks yet on Clinton. But the driver's license question seemed to crystallize that dynamic.

Clinton tried to move on yesterday, accepting an important union endorsement from the American Federation of State, County and Municipal Employees and casting the debate as a case of all the other candidates trying to bloody her. “The Politics of Pile-On” was how her Web site portrayed it.

Republicans were to join the pile.

On his Web site, former Massachusetts Gov. Mitt Romney pasted a headline across a news release: “No Driver's Licenses. Period.”

Former New York Mayor Rudy Giuliani circulated an excerpt from a television interview yesterday in which he declared his opposition to the plan and mocked Clinton for being evasive. Though he now advocates a crackdown on illegal immigration, Giuliani recently has been on the defensive for his past support of illegal immigrants' rights.

Lou Dobbs, the CNN talk show host who has pursued a long-running crusade against illegal immigration, declared that Clinton “is in big trouble.”

Alan Abramowitz, an expert on electoral politics at Emory University, said Clinton's handling of the issue gave her opponents an opening.

“She could have handled it much better,” Abramowitz said. “But instead she's gotten herself into the worst of both worlds. How much long-term damage she's suffered remains to be seen, but this gives Obama and Edwards an opening.”

Gary Jacobson, a political scientist at the University of California San Diego, said he thought the damage would be limited and not long-lasting because “her constituency is not the Lou Dobbs crowd.”