Haley, as a former ambassador, made an impassioned case for the U.S. continuing military and financial aid to Ukraine amid Russia's invasion.

"When you look at the situation, you have a pro-American country that was invaded by a thug," she said. "You want to talk about what has been given to Ukraine, less than 3.5% of our defense budget has been given to Ukraine. If you look at the percentage per GDP, 11 of the European countries have given more than the U.S."

She was interrupted by Ramaswamy, who is opposed to further assistance, and the two had a fiery back-and-forth.

Haley told the political newcomer: "You have no foreign policy experience and it shows."

On Ramaswamy's approach to Putin, Haley said: "This guy is a murderer and you are choosing a murderer."

-ABC News' Alexandra Hutzler

Scott just took a question about national security and turned it into one about immigration, saying our Southern border is the greatest national security threat. Ramaswamy did something similar earlier. If you look at the polling, it’s easy to see why: According to our FiveThirtyEight/Washington Post/Ipsos poll, 36 percent of Republicans identified “controlling immigration” as one of their top issues in the primary — second only to inflation and rising prices.
-Analysis by Nathaniel Rakich of FiveThirtyEight

Ramaswamy came out hitting the other candidates, saying he's the only one who hasn't been bought and sold. When it came to his comments on Ukraine, though, Pence and Haley are hitting back. "You have no foreign policy experience and it shows," Haley said. As Jacob said, his quick rise is drawing attacks, especially on his lack of political experience.
-Analysis by Monica Potts of FiveThirtyEight

Haley tried to go after DeSantis as he was answering a question on Ukraine but it didn't generate the same back-and-forth as with Ramaswamy, and the moderators quickly moved on to another matter. Clearly Ramaswamy -- his lack of political experience and rapid rise in the polls -- has gotten under the skin of the other candidates on the stage and they're going out of their way to take him down a peg even if it means forgoing opportunities against the ostensible polling leader.
-Analysis by Jacob Rubashkin, Inside Elections

As Republican candidates gear up for the debate, many have specific rituals they’ll be doing in preparation.

A campaign adviser for Haley said she will be listening to music, “lots and lots of music: Joan Jett, Queen, Def Leppard and [the] Go-Gos, to name a few.”

DeSantis has spent today with his wife, Casey, and their three children, though a campaign spokesman offered few details about how the family has spent their time.

Hutchinson posted a photo of himself preparing with notepad and laptop in hand.

“Some last minute studying and prep for tomorrow! It’s important to show up and be ready to answer the tough questions, you deserve nothing less than a leader ready to lead on day one,” Hutchinson captioned the photo online.

Pence will plan to spend time in prayer before the debate, while Scott took a tour of the debate stage, which he posted a video of, along with encouragements from his family, to X, formerly known as Twitter.

Others prepared physically, earlier this week.

Ramaswamy posted videos to X of himself playing tennis and him and his wife doing floor exercises in a gym throughout the lead-up week.

Burgum was playing a stress-relieving pickup game of basketball on the eve of the debate, according to a campaign press secretary, when he sustained an Achilles injury that called into question his ability to participate in the event.

He will be participating, albeit on crutches, per a photo posted to his X account.

-ABC News’ Gabriella Abdul-Hakim, Libby Cathey, Abby Cruz, Will McDuffie and Olivia Osteen