New television ads take head-on the criticism that she cannot be trusted and is unelectable. She is directly and repeatedly attacking Sen. Barack Obama (D-Ill.) as too inexperienced for the White House. The message blares from one of her campaign websites: "Experience matters."
She stepped out again Wednesday by sharpening distinctions with Obama on healthcare, challenging his claim to have a plan that would provide universal coverage.
It is a more in-your-face posture than earlier in the campaign when, sitting atop a commanding lead in national polls, Clinton adopted an above-the-fray stance that focused more on attacking Republicans than on challenging fellow Democrats.
Ann Lewis, a senior campaign advisor, said Clinton's sharper tone is an appropriate response to the fact that she has been the target of increasing criticism from her rivals.
"You either ignore it or you respond," Lewis said. "We are in a new phase of the campaign in which the debate among candidates is not happening only on TV debates but has moved to the daily campaign dialogue. She's not going to be on the sidelines."
Indeed, all of the candidates have sharpened their rhetoric as the balloting draws nearer. Obama, despite his signature promise to avoid negative campaigning, has with increasing intensity portrayed Clinton -- the former first lady and now U.S. senator from New York -- as a creature of a discredited Washington establishment. Former Sen. John Edwards of North Carolina has accused her of defending a corrupt political system.
All campaigns tend to get more intense and negative as the voting day approaches. And the stakes could not be higher for the Democratic candidates than in Iowa, which holds its caucuses Jan. 3. Edwards and Obama are counting on a victory in Iowa to give their campaigns money, momentum and publicity to help win subsequent primaries. For Clinton, Iowa could be the last obstacle to her securing the nomination.
"If she wins Iowa, I think the race is over," said Democratic pollster Mark Mellman. "There's really no place else to stop her."
But recent polls show her locked in a three-way tie in Iowa, and her lead in New Hampshire is narrowing. Under those circumstances, it is not surprising she is taking a more aggressive tack, analysts say.
"This is prudent strategy rather than a panic," said Geoff Garin, a Democratic pollster not affiliated with any candidate. "In Iowa and New Hampshire, the Clinton campaign is hearing footsteps behind it. They probably would have been happier to skate through this process above the fray, but . . . it doesn't seem that above-the-fray is a very safe strategy."
Earlier in the campaign, Clinton tended to minimize the differences among Democratic contenders and urged them instead to focus fire on President Bush and GOP presidential candidates.
At Iowa's Jefferson-Jackson Day dinner this month, she said, "I'm not interested in attacking my opponents. I'm interested in attacking the problems of America, and I believe we should be turning the heat on the Republicans."
But her rivals have become increasingly difficult to ignore as they try to portray her as too polarizing to win the general election and accuse her of changing or obfuscating her positions on issues such as trade and the Iraq war. Her latest TV ads take on the allegations that she is untrustworthy and unelectable.
One ad features a man whose son received emergency medical care thanks to Clinton's intervention. "Now, her opponents are saying that Hillary can't be trusted," the man says on camera in the ad. "I trusted this woman to save my son's life, and she did."
Another ad features a barrage of Republican attacks on Clinton and suggests they are evidence that she is the Democratic candidate they fear most.
"The same old Republican attack machine is back," the ad says. "Why? Maybe because they know that there's one candidate with the strength and experience to get us out of Iraq." Clinton began more directly engaging her Democratic rivals after an Oct. 30 debate in which her opponents pummeled her as evasive and inconsistent in answering questions on subjects such as Social Security and immigration policy.
She was in fighting form in the next debate, last week in Las Vegas, when she criticized Obama's health plan as inadequate and accused Edwards of mudslinging.
Since then, her most pointed barbs have been directed at Obama. This week, she expanded her critique of his resume by suggesting, for the first time, that he is not equipped to manage national economic policy without "on-the-job training." On Wednesday, she continued her criticism of his healthcare plan, insisting it does not provide universal care because it does not include a coverage mandate.
Clinton has also belittled Obama's claim that living abroad as a child helped prepare him to manage foreign affairs. "Voters will judge whether living in a foreign country at the age of 10 prepares one to face the big, complex international challenges the next president will face," she said in Iowa this week, in remarks that were transcribed and circulated by the campaign to reporters.
Gordon Fischer, a former Iowa Democratic Party chairman who is supporting Obama, said Clinton's criticism of Obama undercut her pledge at the Jefferson-Jackson dinner not to attack her rivals.
"The problem with Sen. Clinton is she's on both sides of every issue," Fischer said. "Unfortunately, negative campaigning is no exception."
Lewis, Clinton's advisor, said throwing elbows is "never our first choice" of campaign style. But as the criticism of Clinton has gotten increasingly personal, she has to respond in kind, Lewis said.
"New lines of debate have opened up," Lewis said. "We are participating in that debate."