>> announcer: decision 2016. this is nbc "nightly news" with kate snow reporting tonight from austin, texas. good evening from austin, texas. just over 36 hours until polls open here and across 11 other states. it is shaping up to be a pivotal night for so many campaigns. the republican race took on a mean edge today. ted cruz and marco rubio attacking donald trump over everything from his taxes, to his business connections and foreign policy. and trump was on defense, especially when it came to an interview this morning in which trump was asked about a supporter who used to be the grand wizard of the ku klux klan. >> reporter: today's fire storm was not over what donald trump did, but what he didn't do. >> just so you understand, i don't know anything about david duke. >> reporter: failing to disavow david duke in this interview. >> you condemn them and don't want their support? >> i have to look at the group. i don't know what group you're talking about. >> the ku klux klan. >> reporter: duke is not formally endorsed the gop frontrunner but has told his radio audience that voting against donald trump at this point is really treason to your heritage. trump tweeted he did disavow duke. >> i disavow, okay? >> reporter: less than two days before super tuesday, marco rubio pouncing. >> there is no place in the conservative movement for david duke, the ku klux klan or any sort of hatred or bigotry in america. >> i don't understand it, but donald trump refused to disassociate himself and condemn white supremacists. >> reporter: trump also drawing fire this morning for retweeting a quote from a fascist atall january dictator. >> do you want to be associated with a fascist? >> no. i want to be associated with interesting quotes. >> reporter: cruz also accusing trump of not wanting to release his tax returns because of possible mafia ties. >> maybe his taxes show those business dealings are a lot more extensive. >> let me stop you there. that's openly speculative. do you have any facts to support that donald trump has mob ties? >> s&a construction owned by a mobster in jail. >> reporter: the bare knuckle insults flying. alabama senator jeff sessions. >> i am pleased to endorse donald trump for the presidency of the united states. >> reporter: that is trump's first senate endorsement. while a swath of the gop may be trying to stop the billionaire, another part is embracing him. kate? >> gabe gutierrez in richmond, virginia. the republicans vying for the nomination could face a make or break night on tuesday. a loss for example for ted cruz here in his home state of texas could be devastating. holly jackson is live in oklahoma city with a look at the importance of this big vote. >> reporter: super tuesday is when the story line should shift from all the attacks to the arithmetic. adding up the delegates each candidate takes home. nearly half spread out across 11 states. ted cruz campaigning in this state today is calling it a battleground for him. but his must win, well, that's texas, his home state which has the most super tuesday delegates, 155 in all. cruz most likely will pull it off. his campaign tells nbc to watch arkansas too. marco rubio meanwhile spending time and resources in virginia, one of his best shots to notch his first win. in georgia, he's looking to pluck off delegates in those suburban area. john kasich is already looking passed super tuesday to march 16th when ohio votes for the governor, do or die from him. even he acknowledged that donald trump could steam roll on tuesday. for the frontrunner, it's not a matter of which state he will win but how many. trump look dominant in nearly all of them. republicans could wake up wednesday morning to find trump with an overwhelming lead. >> thanks so much. here in texas, argue niezers say they expect a big increase in the number of latino voters this super tuesday. the last exit polls here show one in ten republican primary voters were latino and they're not all voting for their home state senator ted cruz. trump is attracting some hispanic voters. just like juan gomez. he already cast his ballot in early voting here. you already voted right? >> right. i voted for donald trump. >> when you first told me that, you were a little reluctant to tell me. >> well, there's a lot of hispanics that are spiteful or whatever about donald trump. i like donald trump for several reasons. number one, you know, i think we need somebody to manage the country. and he's a businessman and very successful businessman. but the other thing is that he -- he tells it like it is. >> what about the wall? >> i think at one point, we need something that will stop the influx of people coming into the united states. i think it's -- you know, the way the economies are in our two different countries, i think we can manage the people that are here. >> but you want to stop the flow -- >> the flow needs to stop, yes. somebody that's coming to the united states in from mexico, they call it el norte. they're looking for a better way of life. mexico is not providing that life for them. it's fine, but unfortunately there's a lot of bad habit that we have in our society. we supply needs for those people. >> the government? >> yes. >> you told me you're a compassionate man, you're a christian. >> i'm very compassionate. i walk with the lord. but there's certain things that, you know, are important for our country. you know, it's like when you run a business. a business has to be healthy. our nation is not healthy right now. >> juan gomez speaking to me there. trump making some inroads here in texas. the democratic candidates also turned their attention to super tuesday states. with hillary clinton's decisive win in south carolina, especially among african-american voters, bernie sanders faces an arduous path forward. >> reporter: secretary clinton storming through the south after her resounding victory in south carolina, flexing her muscles in nashville today. >> i will stand up and work and fight for you! >> reporter: heroin smashing expectations. she toppled sanders by nearly 50 points and netted close to 90% of the african-american vote, even more than barack obama won over in 2008. all that signaling a potential strong showing come super tuesday. on "meet the press" today, sanders acknowledged the magnitude of the defeat. >> well, we got decimated. that's what happened. among older african-americans it was pathetic. >> reporter: but he also vowed to fight on. that persistence on display at a rally in oklahoma. >> there would be nothing that would give me more pleasure than to defeat donald trump. >> reporter: sanders faces a steep climb. our three new nbc news "wall street journal" polls show clinton topping sanders by nearly 2 to 1 margins in georgia. >> i just don't see a path for ber bernie sanders. assuming nothing legal happens out of the justice department, hillary clinton is going to be the nominee. >> reporter: and clinton is already pivoting to the general election, again taking a broad swipe at donald trump. >> america remains great. but what america needs to do now is become whole. >> reporter: in a rare moment of solidarity, hillary clinton's campaign retweeted senator sanders who condemned donald trump's refusal to disavow former kkk leader david duke. america's black president cannot and will not be succeeded by a hate mongerer. and the man who plays the fictional president on "scandal" campaigned with clinton today and mentioned trump's latest controversy. meanwhile, clinton's e-mails continue to cast a cloud over her campaign this weekend. the state department working to release the final batch by monday's court ordered deadline. donald trump vowing to raise the issues of her e-mails every day if the two face off in a general election. kate? >> kristen, thank you. a suburban virginia police department is mourning the death of a young officer killed in the line of duty just one day after she was sworn in. steve patterson has the story. >> we have three confirmed hits. >> reporter: the call, so unthinkable here, it was called into question. >> i just want to be clear, do we have officers involved in a shooting? >> we have three officers that have been shot. >> reporter: words that confirm the worst. three officers from prince william county police responding to a domestic shooting in woodbridge, virginia, a sleepy suburb of washington, d.c. officers wounded. 28-year-old officer ashley gwendon killed. >> police william county police department is in very deep mourning over the loss. >> reporter: the suspect 32-year-old ronald hamilton, an army staff sergeant captured. >> the accused and his wife were involved in a domestic altercation for some period of time that day. she was shot and killed allegedly by the accused. >> officer gwendon was just sworn in on friday. welcoming words, be safe, at the end of a now tragic tweet. first serving her country six years in the marine corps reserve. >> she clearly had a passion to serve others. >> reporter: now white flowers and black bunting, shock to a department that in nearly four decades had only suffered three line of duty deaths until now. a trail of blue lights in a police procession celebrating a life lost too soon. steve patterson, nbc news. as a fragile cease-fire enters a second day in syria, the international war against isis rages on. one woman has been battling them on her own for over a year. she's a yazidi and isis is threatening to wipe out her people. earlier this week, she was presented with a major international award for her work. >> reporter: she's one of iraq's most adored politicians and the islamic state's most wanted woman. when she's not rallying her people to fight isis, she's helping women and girls escape them. families turn to her for help. >> 11 members of his family are messing. >> women. >> children. >> yes. >> reporter: when isis fighters attacked iraq's yazidis 18 months ago, trapping them on a mountain, she cried out for help in parliament. [ crying ] her people are in crisis. nearly half a million are in refugee camps, hundreds of men disappeared, feared dead. more than 2,000 yazidi women and girls are still missing, held captive by isis. >> those terrorists buying and selling yazidi girls. >> reporter: she smuggles the women and children to safety. jilan escaped five months ago with her sister, but had to leave another sister behind. >> translator: she's only 11 years old. isis is asking for 25 to $35,000 for her freedom. >> reporter: it's dangerous work. >> are you afraid at all? >> no. >> maybe a little bit. >> yeah. >> reporter: what's harder she says is seeing her people suffer while the world turns a blind eye. >> all of them support me, yet you are right. you need support, but nothing happened. >> reporter: so far she's helped rescue more than 1,000 women and girls. >> all of them are looking for me to give hope for them. >> reporter: and nothing, she says, will stop her. nbc news, northern iraq. when "nightly news" continues on this sunday, allowing young children to fire a weapon. we'll take you to one state where lawmakers are everyone's lookin' red carpet ready. my man, lemme guess who you're wearing... toenail fungus!? whaaat?!? fight it! with jublia. jublia is a prescription medicine... ...used to treat toenail fungus. use jublia as instructed by your doctor. jublia is workin' it! most common side effects include... ...ingrown toenail, application site redness,... ...itching, swelling, burning... ...or stinging, blisters, and pain. oh!! fight it! with jublia! now that's a red carpet moment! ask your doctor if jublia is right for you. visit our website for savings on larger size. 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(abdominal pain. urgent diarrhea. it could be ibs-d. new prescription xifaxan is an ibs-d treatment that helps relieve your diarrhea and abdominal pain symptoms. do not use xifaxan if you have a history of sensitivity to rifaximin, rifamycin antibiotic agents, or any components of xifaxan. tell your doctor right away if your diarrhea worsens while taking xifaxan, as this may be a sign of a serious or even fatal condition. tell your doctor if you have liver disease or are taking other medications, because these may increase the amount of xifaxan in your body. tell your doctor if you are pregnant, plan on becoming pregnant, or are nursing. the most common side effects are nausea and an increase in liver enzymes. ask your doctor about new xifaxan. it seems to be all the rage in this nation of snackers. an alternative to chips and chocolate. it's low fat, high in protein, and portable. sales here in texas and across the country are exploding. we're talking about jerky, now perceived by many as a more healthy option. >> reporter: it's an interstate convenience store the size of a warehouse. 120 gas pumps, 34 types of taffy, 26 flavors of fudge. but at bucees, one of the biggest draw is the deli style jerky bar. >> me and my friend made a trip from san antonio. >> reporter: 35 kinds in the glass case. >> jerky sales are exploding. >> reporter: the dried meat is the snack of the moment. sales up 12% last year across the country. americans spending almost $3 billion. >> it's protein. definitely better than potato chips. >> reporter: and that's the allure. high protein, low fat, very portable. >> lean, good energy source, and what's not to like. >> reporter: so popular, one of the nation's hottest franchises, the beef jerky outlet where they even sell krau crawfish and bloody mary flavored jerky. today's jerky has come a long way from those pressed slim jims. now boutique brands with innovative flavors. >> cherry maple. >> reporter: there's also ghost pepper, teriyaki, sweet and spicy. no refrigerator required. but it doesn't mean it will last. >> how quickly will you go through this? >> i'll probably be done with it by the time we get to dallas. >> reporter: hot and dry and fun off the shelf. >> my kids love it. that is nbc "nightly news" for this sunday night. lester holt will be in tomorrow. i'm kate snow. i'll see you tomorrow on msnbc from houston. from all of us here at nbc news, have a great night. she was smart. she was beautiful. >> i can't even tell you how much i loved her. can't even describe the love. >> she walked out her front door and was never seen again. a young mom to two little girls. >> this woman had gone out to get the mail and disappeared in her pajamas. >> and that was just mystery number one. it was a crime right out of the movies. a secret imposter and something sinister. >> oh, high gosh. did this really happen? >> a plot hatched through a virtual world turned suddenly, violently real. >> there was a scream.