Seeking to balance her response to the attacks against her ties to the Obama administration, which is under fire for its response to ISIS, Clinton on Saturday called ISIS a "barbaric, ruthless, violent, jihadist terrorist group" that must be destroyed.
"We have to look at ISIS as the leading threat of an international terror network. It cannot be contained; it must be defeated," she said. "What the president has consistently said, which I agree with, is that we will support those who will take that fight to ISIS."
The two-hour event, which began on a somber note with a moment of silence to honor the victims of the Paris attacks, also offered a crucial opportunity for Clinton to demonstrate the foreign policy qualifications she honed during her time as the Obama administration's top diplomat. The relative inexperience of her rivals -- Vermont Sen. Bernie Sanders and former Maryland Gov. Martin O'Malley -- was also tested.
Both Sanders and O'Malley seized on the foreign policy discussion to criticize Clinton for her vote in support of the Iraq War when she was in the Senate.
"I would argue that the disastrous invasion of Iraq, something that I strongly opposed, has unraveled the region completely and led to the rise of al Qaeda and to ISIS," Sanders said.
O'Malley argued that the problem wasn't simply limited to Clinton's vote for the Iraq invasion, pointing to "cascading effects" that followed.
"We need to be much more far-thinking in this new 21st-century era of nation-state failures and conflict. It's not just about getting rid of a single dictator," he said.
Clinton, meanwhile, is certain to be criticized for pointing to the terrorist attacks of September 11, 2001, in defending her acceptance of Wall Street contributions.
"I represented New York on 9/11 when we were attacked. Where were we attacked? We were attacked in downtown Manhattan, where Wall Street is," she said. "I did spend a whole lot of time in their effort to rebuild. That was good for New York, it was good for the economy, and it was a way to rebuke the terrorists who had attacked our country."
The Democratic candidates contrasted themselves against their Republican counterparts on the issue of the refugee crisis in the Middle East. Though many GOP presidential candidates have said the U.S. shouldn't accept refugees into the country, the Democrats argued that it's America's responsibility to accept those fleeing violence in countries like Afghanistan and Syria, with proper screening.
Calling for "as careful a screening and vetting process as we can imagine," Clinton, who has previously stated that the U.S. should accept as many as 65,000 new refugees, said, "I do not want us to in any way inadvertently allow people who wish us harm to come into our country."
Sanders said that he didn't want to offer a "magic number" but that it was the United States' "moral responsibility" to accept refugees in conjunction with its allies in Europe and the Middle East.
O'Malley also reiterated that the country should accept as many as 65,000 refugees.
In one part of the debate that Republicans have quickly seized on, no Democratic candidate used the term "radical Islam" to describe terrorism. This phrase is preferred by Republicans, who have accused Democrats of shying away from a forthright description of ISIS.
"I don't think we're at war with Islam. I don't think we're at war with all Muslims," Clinton said. Cautioning against painting with "too broad a brush," she added: "We are at war with violent extremism."
Sanders, meanwhile, said he didn't believe the exact term was important.
Though much of the debate focused on national security in light of the tragic events in Paris, Clinton also sparred with her rivals on hot-button domestic issues like financial regulatory reform and gun control.
Progressives and Wall Street reform advocates have consistently hit Clinton for her perceived closeness with Wall Street, particularly as she's raised large sums of money from wealthy donors in the financial industry.
"I've laid out a very aggressive plan to rein in Wall Street," Clinton said, touting a plan that she said targets not only the big banks but the shadow banking industry as well.
Asked to react to Clinton's answer, Sanders shot back: "Not good enough."
The Vermont senator said he was the only candidate on stage who did not have a super PAC, vowed to break up the big banks and said voters understand that any candidate who accepts contributions from special interests are influenced by them. "Everybody knows that," he said.
O'Malley also hit Clinton for not backing the reinstatement of Glass-Steagall, the Depression-era law that split commercial and investment banking. Wall Street reform advocates favor bringing back a modern version of the law.
"I won't be taking my orders from Wall Street," O'Malley said.
Later in the debate, Clinton went after Sanders for supporting a measure that she said gave immunity to gun makers and sellers, labeling it a "terrible mistake."
Sanders pushed back, saying he has voted repeatedly for background checks for gun buyers.
The issue of Clinton's use of a private email server during her time at the State Department also surfaced, but briefly.
As he did in the first Democratic debate, Sanders said that he was "sick and tired" of discussing the controversy and that he would prefer that the media focus on "why the middle class is disappearing."
Letting out a laugh, Clinton said, "I agree completely. I couldn't have said it better myself."
Asked whether Democrats can feel confident that no other shoe will drop, Clinton responded, "I think after 11 hours, that's pretty clear" — a reference to her day-long testimony on Capitol Hill where she largely avoided fresh, negative headlines.
Changes for Democrats
A lot has changed since Clinton, Sanders and O'Malley met for their first showdown in Las Vegas last month.
There were five candidates on stage at the time. Since then, two have dropped out.
Last month, the possibility of Joe Biden jumping into the race and upending the party's nomination process loomed large; now, the country knows that the vice president will not pursue another White House bid.
And Clinton has had fresh momentum heading into the debate. After a strong first debate performance, her poll numbers have ticked up, and she's widened her lead over Sanders.
And on Saturday, it was clear that Clinton sought to distinguish herself as the candidate with the most experience on the global stage, including in the war against terrorism. This distinction will no doubt only become more stark in light of the terrorist attacks in Paris.
When the candidates were asked to describe a crisis they've confronted that shows they've been tested, Clinton used the opportunity to remind viewers that she was secretary of state and adviser to Obama in 2011 when U.S. Special Forces killed al Qaeda leader Osama bin Laden.
"I recommended to the President that we take the chance to do what we could to find out whether that was bin Laden and to finally bring him to justice," Clinton said. The "excruciating experience," she added, "really did give me an insight into the very difficult problems presidents face."