While liberals find her far too right-leaning on the hot-button issue of Iraq, conservatives have stamped Clinton as a liberal who would favor big government "tax and spend" politics and lenient social policies.

Although still the hands-down favorite for her party's nomination, Clinton's stance in the debate leaves her newly vulnerable, pundits said.

"Maybe she's a bit overconfident about the nomination. She's running a general election strategy ... she wants to stay moderate," said Sabato said.

"I think she's going to have a much harder time getting the nomination than she thinks."

He predicted one challenge will be locking up the votes of centrist Democrats, with whom he said she has an even bigger problem than with left.

"There's a broader group who would never boo her ... They all seem to say, 'Oh, I love Hillary, I think she's terrific. But of course, we can't nominate her because she can't win the general election'," said Sabato.

At last week's gathering, Clinton's fellow senator John Kerry -- one of the Democrats waiting in the wings should she misstep -- garnered cheers for backing a US troop withdrawal proposal within months.

But while Kerry -- the 2004 Democratic presidential nominee -- and several other prominent party members remain in the hunt, experts said Clinton is still the most viable contender for the nomination.

"She has put herself in the position that is most likely to win a presidency for a Democrat," said Thomas Mann, an analyst with the Brookings Institution in Washington.

"She's going to have to fight for it," said analyst Stephen Hess, also of Brookings, "but she certainly starts with greater name recognition, more money and a more coherent group of supporters than anyone else."

Mann said Clinton would be well-advised to stay the course, even if it prompts some chafing on the left.

"Hillarys problem with Iraq is more with activists than Democratic primary voters," he said.

To fine-tune her stance at this point, he added, would be "to make it seem that she'll move things for votes rather than for principle," he said.

"Her biggest challenge is persuading Democrats that she can win a general election in spite of the withering attack Republicans are certain to launch against her," he said.

"Thats why there remains a substantial market for someone other than Hillary."