Follow this CNN Republican debate live blog for all the best moments from the last GOP debate of 2015 on the stage and on social media.
After the undercard debate, the prime-time showdown focuses on keeping America safe. Watch live on CNN TV or, if you're in the United States, try CNNgo. Go to CNN.com/predict to predict which way the candidates' odds will move throughout the debate.
Your host for the evening is CNN Politics reporter Tal Kopan, and as you're following the event, use #GOPDebate to engage with all the action on social media.