Hillary Clinton's big night on the debate stage

Hillary Clinton delivered a poised, polished performance in the campaign's first Democratic presidential debate, firmly defending herself against claims that she flip flops for political gain and likely quelling nerves in her own party after a stumbling start.

Her confident demeanor on the debate stage in Las Vegas may also dampen speculation that there is a place in the race for Vice President Joe Biden, who is still agonizing over a decision about whether to mount a late presidential run.

The debate was an important pivot point in the Democratic campaign, which until Tuesday had unfolded largely at arms length between the candidates. The race has been dominated by a perception that once again, Clinton is a leaden candidate who, just as in 2008, is in danger of losing her status as a front-runner to an upstart outsider -- in this case Vermont Sen. Bernie Sanders.

Clinton produced a more convincing rationale for why she should be President than she has done so far, dismissing the idea she was motivated mainly by restoring the Clinton political machine. She argued she has the vision and experience to enforce change, and drew an analogy between her own relentless refusal to admit defeat with the resilience of America itself as the nation battles back after a tough recession.

"The issue is not whether you get knocked down, it's whether you get back up," said Clinton, who also rejected the critique that her changing positions on the vast Trans Pacific Trade deal, the Keystone XL Pipeline and gay marriage meant she is just a hostage to shifting political winds.

READ: Fact-checking the candidates

"I have been very consistent," Clinton said. "Over the course of my entire life, I have always fought for the same values and principles, but, like most human beings, including those of us who run for office, I do absorb new information. I do look at what's happening in the world."

Branding herself as a "progressive" who can get things done, Clinton also painted herself as the kind of candidate who could break the Washington gridlock that has some voters turning to outsider candidates in a tumultuous campaign season.

"I know how to stand my ground, and I know how to find common ground," Clinton said.

While Clinton appeared to have made the biggest splash in the debate, it sometimes takes several days for voter perceptions to gel. And should Clinton win the nomination, her email situation, the controversy over Benghazi, and her role in some of the foreign policy missteps of the Obama administration will come under much more testing scrutiny from a Republican nominee than from her fellow Democratic candidates.

She did have a tough moment in the debate when she tried to explain her recently-announced opposition to the Keystone pipeline by saying: "I never took a position on Keystone until I took a position on Keystone."

But it appeared that Clinton, who betrayed few signs of rust after enduring 25 Democratic debates during her 2008 campaign, had satisfied her goals of appearing as the most presidential candidate on stage -- and of avoiding any major gaffes that could further damage her poll numbers.

WATCH: Key quotes from the debate

Sanders also put in a strong performance and was largely true to his word that he would not mount direct attacks but try to confine the debate to the issues. But in the process, he and the other candidates weren't able to subject Clinton to uncomfortable scrutiny over her vote to authorize war in Iraq, which still rankles the party's base voters, or her failures as secretary of state.

Though he was passionate as always, his style appears more suited to the big rallies before huge crowds he has been holding in sports arenas than the more intimate debate stage.

In fact, Sanders rode to Clinton's rescue on the biggest vulnerability of her campaign -- the controversy over the private email server she used as secretary of state, -- saying it was a distraction and "the American people are sick and tired of hearing about your damn emails!"

David Axelrod, who eight years ago was a member of Barack Obama's brain trust that felled Clinton, said her performance was impressive.

"I think she did very very well. She was poised, she was passionate and I think she was in command," said Axelrod, now a CNN political analyst.

Clinton and Sanders, reflecting their poll numbers, which have them in first and second place, appeared the most substantial figures on stage. Former Maryland Gov. Martin O'Malley, despite some strong interventions, appeared not to land the serious blow that he needed to ignite his campaign.

The other two candidates, former Virginia Sen. Jim Webb and former Rhode Island Gov. and Sen. Lincoln Chafee, struggled. On one occasion, for instance, Chafee blamed a Senate vote that now seems a liability on the death of his father.

While Sanders came to Clinton's rescue on the email situation, the former secretary of state didn't give him a pass on his philosophy of Democratic socialism that many in the party fear is too radical to pass muster in a general election. She also pressed Sanders on the issue of gun control following a spate of mass shootings.

WATCH: Pictures of the Democratic debate

After Sanders argued that his vision for politics was akin to Scandinavian nations with strong health care systems and social safety nets, Clinton pounced.

"I love Denmark!" she said, but argued that they were running for president of the United States of America and such economic policies would not work here.

The former secretary of state also slammed Sanders for his positions on guns, including voting against legislation such as the Brady Bill. Clinton was asked whether Sanders had been tough enough on regulating firearms.

"No, not at all," Clinton said. "This has gone on too long and it is time the entire country stand up against the NRA."

But Sanders hit back, telling Clinton sharply that "all the shouting in the world is not going to do what I hope all of us want," namely more restrictions on firearms.

Sanders also seemed to score points when he implicitly turned on Clinton over her ties to big business and rich donors.

"In my view, Congress doesn't regulate Wall Street, Wall Street regulates Congress," Sanders said.

READ: Clinton and Sanders finally face off

In one of his few effective moments, Chafee seemed to take a clear shot at Clinton and her struggles to overcome the email controversy, saying that in all his years of public service, he had shown "high ethical standards" and had not been involved in any scandals.

The candidates also differed on foreign policy.

Clinton defended her role in engineering a "reset" of relations with Russia while secretary of state and said things had changed only when Vladimir Putin returned to the presidency. She said the United States must stand up to Putin's "bullying" and must take "more of a leadership position" to help end the bloody civil war in Syria.

That prompted Sanders to slam the war as a "quagmire in a quagmire" and argued that it was triggered by the war in Iraq -- a clear reference to Clinton's decision as a New York senator to authorize the war in Iraq in late 2002.

Seeking to prevent yet another presidential election being consumed by a debate over that fateful vote, Clinton invoked President Barack Obama to defend herself.

"After the election (in 2008) he asked me to become secretary of state. He valued my judgment and I spent a lot of time with him in the Situation Room going over some very difficult issues."

Both Sanders and O'Malley hit Clinton over her call for a no-fly zone in Syria, with the former Maryland governor warning it could cause a clash with Russian forces operating over the war-torn Middle Eastern nation and that as president, he would be less likely to use a "military tool" than she would be.

Clinton reminded O'Malley that he endorsed her for president in 2008.

Republicans have already held two fiery debates dominated by the presence of Donald Trump.

Trump was one of the few Republicans mentioned in passing in the debate. He was live-tweeting throughout, warning that the Democratic candidates were "all very scripted and very rehearsed" and at least two should not have been on stage.

In an election that has elevated politicians seen as outsiders and non-politicians, Clinton sought to play up her own historic status.

"I can't think anything more outsider than electing the first woman president."

She also took aim at the perception that electing her would perpetuate the kind of dynastic politics that many Americans dislike.

"I would not ask anyone to vote for me based on my last name," she said. "I am certainly not campaigning to become president because my last name is Clinton. I am campaigning because I think I have the right combination of what the country needs at this point and I think I can take the fight to the Republicans because we cannot afford a Republican to succeed Barack Obama as president of the United States."