From the Hillary Clinton email scandal, to Planned Parenthood, to the Black Lives Matter movement, their responses generated plenty of buzzed-about moments. Among the field featuring Clinton, Bernie Sanders, Martin O'Malley, Lincoln Chafee and Jim Webb, it was clearly Clinton and Sanders who stood out.
Here are the top seven moments from CNN's Democratic debate.
The biggest applause line of the night went to Sanders -- but it actually was a point for Clinton.
She was defending herself from the onslaught of questions about her use of a private email server as secretary of state, saying the American people care more about the issues facing the country. And it was Sanders who leapt to her defense.
"Let me say something that may not be great politics, but I think the secretary is right, and that is that the American people are sick and tired of hearing about your damn emails," he said.
"Me too, me too," Clinton laughed.
"Enough of the emails, let's talk about the real issues facing America," he said, to a partial standing ovation.
2) The Benghazi committee
Not surprising anyone, Clinton continued to attack the Republicans for convening a special committee in Congress to investigate the Benghazi attack -- using recent comments by House Majority Leader Kevin McCarthy that made it seem like the committee had a purely political purpose in trying to damage Clinton.
Clinton said she's looking forward to her public testimony before the committee next week -- but that doesn't change her concerns about the panel.
"This committee is basically an arm of the Republican National Committee. It is a partisan vehicle as admitted by the House Republican Majority Leader, Mr. McCarthy, to drive down my poll numbers," Clinton said.
But: "I am still standing," she said, to applause.
Pressed by CNN's Anderson Cooper, she said she wasn't saying the inquiry into the attack in Libya "wasn't legitimate." But, she added, "I think it would be really unfair not to look at the entire picture. This committee has spent $4.5 million of taxpayer money. I think it's pretty clear what their obvious goal is."
Clinton's best line of the night may have been one that was only two letters long.
On the topic of her emails, Chafee repeated a refrain he came back to many times during the debate, that "we have to repair American credibility."
"Credibility is an issue," he said.
Moderator Anderson Cooper asked: "Secretary Clinton do you want to respond?"
"No," she said, and the Vegas audience ate it up.
4) Planned Parenthood
The Democratic front-runner turned a question about paid family leave -- and Republicans' criticism of how she'll pay for her plan -- into an attack on the GOP and its full-court press against Planned Parenthood, an issue sure to ignite her base.
"They don't mind having big government to interfere with a woman's right to choose and to try to take down Planned Parenthood," she said. "They're fine with big government when it comes to that -- I'm sick of it."
The line, once again, got major applause.
"We should not be paralyzed by the Republicans and their constant refrain, 'big government this, big government that,' except for what they want to impose on the American people," she continued. "I know we can afford (paid leave) because we're going to make the wealthy pay for it."
5) 'Black lives matter'
One of Sanders' biggest challenges in pulling close to Clinton in national polling is his ability to capture minority voters -- something he has been dedicating plenty of time to on the trail.
Given the opportunity in the debate, Sanders made no attempt to hedge in response to a question from Facebook asking, "Do black lives or do all lives matter?"
"Black lives matter," Sanders said unequivocally -- a stark contrast with Republicans who have taken the "all lives matter" approach.
Sanders said the reason "those words matter" is that it is African-Americans who are scared of their kids getting shot or innocent black Americans ending up dead in jail, like Texan Sandra Bland.
"We need to combat institutional racism from top to bottom, and we need major major reforms in a broken criminal justice system in which we have more people in jail than China," Sanders said. "I intend to tackle that issue, to make sure our people have education and jobs rather than jail cells."
6) A weak moment
Clinton had a slight stumble on explaining her position on the Keystone Pipeline, which she recently came out against.
"I never took a position on Keystone until I took a position on Keystone," she said, echoing former vice presidential candidate John Kerry's much-pilloried "(I) actually did vote for the $87 billion before I voted against it" Iraq war flub.
7) Thank you, Martin
Responding to a question about O'Malley's criticism of her foreign policy, Clinton made a backhanded compliment against the former governor.
"You know, I have to say, I was very pleased when Gov. O'Malley endorsed me for president in 2008, and I enjoyed his strong support in that campaign," she said. "And I consider him, obviously, a friend."
O'Malley did not directly respond.