(CNN) Hillary Clinton , Bernie Sanders and Martin O'Malley met for the second Democratic presidential primary debate on Saturday night, an event that finally saw a fight between the front-runner and her chief opponent, but also coming a day after a deadly terror attack that shocked the world.

From left, Democratic presidential candidates Bernie Sanders, Hillary Clinton and Martin O'Malley prepare to debate at Drake University in Des Moines, Iowa, on Saturday, November 14. It was the party's second presidential debate.

From left, Democratic presidential candidates Bernie Sanders, Hillary Clinton and Martin O'Malley prepare to debate at Drake University in Des Moines, Iowa, on Saturday, November 14. It was the party's second presidential debate.

Here are the six key takeaways from the debate:

1. Clinton shows daylight with Obama on ISIS

Clinton distanced herself from President Barack Obama's now-controversial comment in an interview Thursday that the U.S. had "contained ISIS." During Saturday's debate, Clinton asserted that ISIS "cannot be contained" and must simply be "defeated."

As she has in the past, Clinton also suggested that she had argued "early on that we needed to find a way to train and equip moderates." Clinton reportedly argued for a more forceful administration plan to help the Syrian opposition early on in the civil war that has since exploded.

2. Sanders finally brawls with Clinton...

The Vermont senator in the first debate appeared unprepared or unwilling to go after Clinton with any real vigor.

But Saturday night, Sanders suggested Clinton is in the pocket of Wall Street and tied her vote to authorize the war in Iraq to the rise of ISIS. Clinton, meanwhile, knocked Sanders on his mixed record on guns and suggested his policy proposals are too simplistic.

In the most forceful exchange of the night, Sanders pointed to the millions of dollars in donations Wall Street has funneled to Clinton's campaigns over her political career.

"Why over her political career has Wall Street been a major, the major campaign contributor to Hillary Clinton? Maybe they're dumb and they don't know what they're going to get, but I don't think so," Sanders said. "I have never heard a candidate, never, who has received huge amounts of money from oil, from coal, from Wall Street from the military industrial complex, not one candidate -- 'Oh these, these campaign contributions will not influence me.' But why do they make millions of dollars of campaign contributions? They expect to get something, everybody knows that."

Clinton responded by accusing Sanders of impugning her "integrity," before claiming that Wall Street has supported her because of the work she did to rebuild the Financial District after it was hit in the 9/11 attack on the World Trade Center.

As she did in the first debate, Clinton hit Sanders on guns, calling the Vermont senator's vote to shield gun makers from some lawsuits a "terrible mistake" and urging Sanders to admit as much, as she has done regarding her Iraq vote.

Sanders responded by suggesting there's little daylight between himself and Clinton and O'Malley on guns.

3. ...but he still holds back

Sanders didn't take the gloves off completely during Saturday night's debate in Iowa.

Instead, he took a pass on one of the biggest points of contention of the 2016 cycle: Clinton's record as secretary of state.

Given a chance to slam Clinton's tenure, Sanders demurred, instead pivoting to his "disagreement" with Clinton over her vote in favor of the Iraq War in 2002, more than six years before she became secretary of state.

Republicans are already picking apart Clinton's track record as secretary of state, but Sanders' simply wouldn't take the bait.

It was reminiscent of Sanders' "damn emails" moment in the first Democratic debate, when he said Americans are tired of hearing about the controversy over Clintons' use of personal email during her time as secretary of state.

Photos: The first Democratic debate Photos: The first Democratic debate Democratic presidential candidates take the stage before debating in Las Vegas on Tuesday, October 13. From left are former U.S. Sen. Jim Webb, U.S. Sen. Bernie Sanders, former Secretary of State Hillary Clinton, former Maryland Gov. Martin O'Malley and former Rhode Island Gov. Lincoln Chafee. Hide Caption 1 of 10 Photos: The first Democratic debate An audience member watches the debate, which was the first Democratic debate of this election cycle. Hide Caption 2 of 10 Photos: The first Democratic debate Sanders speaks during the debate. CNN's Mark Preston said Sanders' opening remarks "hit on all of the hot-button liberal issues: Take back the government from billionaires, climate change. He all but said it is time for a revolution." Hide Caption 3 of 10 Photos: The first Democratic debate Clinton is the national front-runner in the Democratic race. "I would not ask anyone to vote for me based on my last name," she said during the debate. "I'm campaigning because I think I have the right combination of what Americans are looking for ... and I can take the fight to Republicans." Hide Caption 4 of 10 Photos: The first Democratic debate Webb listens to moderator Anderson Cooper during the debate. Webb is a former Marine who also served as secretary of the U.S. Navy. "You may be sure that in a Webb administration, the highest priority will be the working people who every day go out and make this country stronger at home, and who give us the right reputation and security overseas under a common-sense foreign policy," Webb said. Hide Caption 5 of 10 Photos: The first Democratic debate O'Malley faces the camera while delivering remarks. He went after Sanders on gun control early in the debate, and -- in what could be interpreted as a veiled swipe at Clinton -- he said, "I am very clear about my principles." Hide Caption 6 of 10 Photos: The first Democratic debate Chafee touted his experience, saying he is the only candidate who has been a mayor, senator and governor. "I have had no scandals. I've always been honest. I have the courage to take the long-term view, and I've shown good judgment," he said in his opening statement. Hide Caption 7 of 10 Photos: The first Democratic debate One of the debate's memorable moments was when Sanders and Clinton shook hands following Sanders' take on the Clinton email scandal. "Let me say something that may not be great politics, but the secretary is right -- and that is that the American people are sick and tired of hearing about the damn emails," Sanders said. "Enough of the emails, let's talk about the real issues facing the United States of America." Hide Caption 8 of 10 Photos: The first Democratic debate Audience members watch the debate. Hide Caption 9 of 10 Photos: The first Democratic debate The Democratic field this year is less than half the size of the Republican field. Hide Caption 10 of 10

4. The moments that could come back to haunt Clinton

However, Clinton's response to Sanders -- when she beat back the suggestion that she is influenced by Wall Street donors -- could really come back to bite her.

Clinton explained her connection to Wall Street by tying her relationship to her role in helping to rebuild New York's financial district after the 9/11 attacks.

Twitter was ablaze Saturday night over the response, and the Republican National Committee was quick to blast out a best-of compilation of political observers' reactions.

It's not the only moment that could come back to haunt Clinton -- especially if she faces a younger GOP nominee, like Sen. Marco Rubio of Florida.

Clinton at one point said she is "from the '60s" -- a moment in the debate that could be replayed in political ads down the line suggesting she is part of the past, not the future, of American leadership.

5. Paris sets the tone

The debate Saturday night began with the candidates pausing on stage, taking a moment of silence to remember the victims of the terrorist attacks that ripped Paris apart just a day earlier.

Clinton said while "our prayers are with the people of France tonight...that is not enough" and called for better coordinated efforts to root out ISIS, the radical group that claimed responsibility.

She said Americans should see the terrorist attack as a reminder that the election "is not only about electing a president, it's also about choosing our next commander in chief."

Sanders made brief note of the terrorist attacks at the top of his opening statement, but quickly pivoted to the core message of the campaign: "a rigged economy" that benefits billionaires.

Still, Sanders made a bold claim in his reference to Paris: "Together, leading the world, this country will rid our planet of this barbarist (sic) organization called ISIS."

And O'Malley, after saying his heart goes out "to the people of France in this moment of loss," quickly called for "fresh thinking" and "new approaches" -- a definitive nod to his youth and the generational contrast the 52-year-old offers to Clinton's 68 years and Sanders' 74.

All three candidates refused to say the fight was with radical Islam, instead focusing on using the word "jihadist" to describe the threats spotlighted in the Paris attacks.

6. O'Malley gets a zinger, then shrinks away

O'Malley delivered several strong one-liners throughout the night, notably when he slammed Republican front-runner Donald Trump as a "carnival barker" for his immigration policies.

But O'Malley also missed a couple of key moments where he could have shined.

His central contention is that it's time for a new generation of leadership -- meaning no more baby boomers like Clinton. But he lacked a strong, convincing response to one of the debate's final questions: When have you been most tested in your life, and how did it prepare you for the presidency?

O'Malley's response conceded that he is untested -- that nothing he's been through as mayor of Baltimore or governor of Maryland comes close to the crises he would face as President.

Trump later responded to O'Malley's insult on Twitter by calling him a "clown."