since the paris and san bernardino terror attacks. and comes about a week after trump called for a ban on muslims entering the u.s. the debate will keep national security at the forefront. >> the vast majority of people that are trying to come are people that we just don't have information on. this is an issue you have to be right 100%. >> reporter: now, marco rubio will be another candidate to keep an eye on tonight. he's performed well in past debates. his team is hopine ining for an strong night. their attitude is why try to fix what's not broken? as for trump and cruz, the question isn't so much whether trump will try to hit cruz but whether and how cruz will hit back. alisyn, chris? >> you did the right thing, athena, conflating, truz, cruz and trump. well played. well done here at 100 o'clock in