>>> president trump pushg back after that vulgar slur uproar. >> i'm not a racist.least racist person. >> tonight, a new divide over what he said in the oval office. >>> serena williams revealing a life-threatens scare after the birth of her daughter. her warning about a hidden health risk and the importance

>>> president trump pushg back after that vulgar slur uproar. >> i'm not a racist. i haven't the least racist person. >> tonight, a new divide over what he said in the oval office. >>> serena williams revealing a life-threatens scare after the birth of her daughter. her warning about a hidden health risk and the importance of listening to your body. >>> and an alert from cvs. >>> a firefighter's heroic catch. >> announcer: this is "nbc nightly news" with lester holt. >>> good evening, everyone, and thank you for being with us. no one should have to go through what the people of hawaii experienced this weekend, receiving what amounted to a doom's day message. given minutes to find shelter from an imminent missile attack. the words "this is not a drill" emblazoned on their phones. we now know it was a mistake. an investigation centers on a state command center just outside ho lnolulu. a place we were given exclusive access to just a day before that false alert was triggered to see the inside of hawaii's early warning system, and to speak to those who sound the warning