Here are a few of the most memorable lines. (For the blow-by-blow, check out the CNN live blog
Ohio Gov. John Kasich on why he stays out of the mud on debate nights: "I have never tried to go and get into these kind of scrums that we're seeing here on the stage and people say everywhere I go, 'you seem to be the adult on the stage.'"
Rubio on why he decided to insult Trump on the trail: "For the last year Donald Trump has mocked everybody with personal attacks. He has done so to people sitting on the stage today. He has done so about the people who are disabled. He has done it about with every candidate in this race. If there is anyone that has deserved to be attacked that way, it's Donald Trump for the way he has treated people in the campaign.
Trump responds to Rubio's suggestion he wouldn't answer a policy question: "Don't worry about it little Marco, I will."
Trump on whether he would be willing to negotiate on his Mexican border wall promise: "The wall's 50 feet high. Is it going to be 45 feet or 40 feet? That could very well be. There's always give and take. We need give and take in government, you're never going to agree on anything."
Trump making nice to Megyn Kelly: "Nice to be with you Megyn. You're looking well."
Trump on the torture debate and what he'd do: "Can you imagine these people, these animals over in the Middle East that chop off heads, sitting around talking and seeing that we're having a hard problem with waterboarding? We should go for waterboarding and we should go tougher than waterboarding."
Cruz jabs Trump: "I think the American people understand that yelling and cursing at people doesn't make you a tough guy."
Rubio responding after Trump said it was important for leaders to be flexible: "There is a difference between flexibility and telling people whatever you think you need to to get them to do what you want them to do."
Cruz after another pitched battle between Trump and Rubio: "Megyn, let me just ask the voters at home, is this the debate you want playing out in the general election?"
A frustrated Kasich: "Let's stop fighting!"
Rubio on water crisis in Flint, Michigan: "I give the governor credit, he took responsibility for what happened."
Cruz to Trump: "Donald, please, I know it's hard not to interrupt. Breathe, breathe, breathe. You can do it, breathe, I know it's hard, I know it's hard."
Rubio interjects: "When they're done with the yoga, can I answer a question?"
Cruz: "I really hope that we don't see yoga on this stage."
Rubio: Well, [Trump's] very flexible so you never know."