The sheriff calls it a crime, the fbi said it must be searched for explosives. In all, 25 people linked to the occupation have now been indicted on federal felony charges. Lester . Joe fryer in oregon, thank you. A major endorsement for Hillary Clinton is spotlighting the critical battle under way for africanamerican votes in South Carolina. A february 27th democratic primary there will be bern i sanders first cast in the south, and before a large number of black voters. Today clinton, who polls show hold a substantial lead among black voters got an important shot in the arm from a civil rights icon, who to sanders delivered just a shot. Nbcs Kristen Welker reporter as Hillary Clinton and Bernie Sanders prepare to face off in milwaukee tonight, there are already fireworks. Theres no one else better to be prepared to be president of the United States of america than Hillary Clinton. Influential political arm backing clinton today. It was congressman john lewis who delivered a major blow to sanders, questioning how active he was in the civil rights movement. I never saw him. I never met him. I was involved in the sitins, the freedom ride, but i met president clinton. Reporter the sanders campaign, bernie is a great admirer of lewis. Releasing this endorsement video featuring the young daughter of eric garner who died after police put him in a choke hold in 2014. To go up against the criminal justice system. Thats why im for bernie. Reporter all underscoring the importance of the african vote, like South Carolina, where clinton leads sanders among africanamericans 74 to 17 . One challenge for sanders, his complicated relationship with president obama, on display during an kasi hunt where they discussed the gap. You dont think president obama has successfully closed that gap . No, i dont. I think hes made the effort. When i talk about a Political Revolution is bringing millions and millions of people into the political process. Reporter the Clinton Campaign firing back. Considering how little senator sanders has to show for his 25 years in congress, the idea that he would be giving leadership lectures to president obama is absurd. Reporter our latest poll shows president obamas Approval Rating among africanamericans in South Carolina is at 92 . So expect secretary clinton to again embrace him tonight in what could be the most contentious debate yet. Lester . Kristen, thank you. The republicans face off in South Carolina a week earlier than the dems, a week from saturday. Tonight much of the fight to take down the highflying donald trump is taking place ted cruz who won the first contest in iowa is trying to bounce back from his loss this week in New Hampshire with an aggressive ground game and a direct attack on trumps conservative credentials. With more, heres hallie jackson. Reporter matt wells quit his sales job in iowa to sell ted cruz instead alongside 10,000 volunteers in South Carolina. I can get another job when i get back. I cant get another country. Its a risky move, quitting your job ill go back to iowa and go back to work and all that. Try to help ted win here first. Reporter wells is one of nearly 10,000 volunteers here in South Carolina, making some 25,000 phone calls a day. Part of the organization cruz is depending on to topple donald trump here, like he did in iowa. The state of South Carolina, i dont think people are a republican candidate whos pushed partial birth abortion, who wont defend marriage. Strategy, paint trump as too liberal, with more ads like this one on the way. Republican. Reporter for his part, trump seems to be playing a more game than before. Its going to be such an unbelievable week and a half. Reporter but in the more mannerly south, his more colorful language may be a big turnoff. He gets the nomination theyre going to sue his [ bleep ] off. Reporter as the focus group found. Its crass. Its nonprofessional. A leading president ial candidate saying profanity from a stage. Reporter marco rubio and jeb bush, meanwhile, taking shots at the frontrunner how do you think donald trump going to washington will solve anything. Jeb bush has no Foreign Policy experience, period. Reporter trying to prove South Carolina isnt simply a twoman underscoring that point, a new cruz ad slamming rubio for being nothing more than a pretty face. This race getting roughandtumble already, with nasty new robocalls. In a new twist, jeb bush is getting backup on the trail from his brother, former president george w. Bush making his Campaign Debut on monday. Lester . Hallie, jackson, thank you. Its always there, lurking, and now the dreaded polar vortex is heading south, bringing with it the coldest air of the season for tens of millions of us. Al roker joins us with the details. Yeah, lester, it will be potentially deadly weather coming in. The polar vortex is already there, but it will shift over to the northern atlantic. The jet stream dips to the south. That means that cold air spills south of the canadian border, into the northeast, and the midwest, bringing some of our colder temperatures that we have seen yet. Bismarck tomorrow will feel like 7, minus 7 in minneapolis. 13 in cleveland. As we get into saturday morning, digits and below. And we bottom out sunday morning, records possible in boston with minus 5, 2 in new york city, 4 in rochester, 1 in pittsburgh, roanoke 10. You get out west, its going to feel like a different season. From seattle all the way to roswell and down to san diego, it will actually feel like temperatures in april and may. So weve got two Different Countries depending on where you live. Al, thanks. Good to have you here. The International Olympic committee tried to reassure the world today that all measures are being taken to fight the zika virus ahead of the games in rio. But u. S. Officials are taking their own precautions as we hear from a star athlete casting doubt on whether shell compete. The outbreak has led to an emergency appeal from top u. S. Officials, health officials. As our rehema ellis reports. Reporter puerto rico could be the next hot spot for the zika virus, warns the cdc, senate today. At some point we may well see tens or hundreds of thousands of zika infections in puerto rico. Reporter this news as the u. S. Olympic committee announced its hiring two Infectious Disease experts to advise the 500 athletes hoping to compete in brazil. Including soccer star hope solo. If i had to decide today, i would not go. Fortunately, the summer olympics are about six months away. I think we have time to get our doubts and questions answered. Reporter the soccer teams will compete in areas even more vulnerable to zika than rio. One is near the amazon rain forest. Another in an area where the number of zika cases are especially high. I dont think soccer being so close to the rain forest where theres more mosquitoes. I take my health very seriously. We all do. Reporter new research has found zika to babies born with microcephalus. Olympic athletes have competed while pregnant, there were five during the london games in 2012, including gold medalest kerry walsh jennings. Well be waiting to hear what steps will be taken to make sure everythings safe and secure. Reporter with women making up half the american team, the countdown to the olympics is on. Rehema ellis, nbc news, new york. A California Utility Company now says its finally stopped the leak from a ruptured well that has been spewing massive amounts of natural gas into the air near los angeles. Making people sick and forcing thousands of families from their homes in porter ranch. Its been leaking for nearly four months. Invisible to the naked eye, but the giant cloud apparent in infrared images. The plug is a temporary fix, but if it holds, it will be cemented closed. They face a lawsuit over the investigations in all nato is intervening in the massive refugee crisis sparked by the war in syria. Its deploying patrol boats to intercept migrant smugglers. As many flee syria, others are trapped, including hundreds of thousands in syrias largest city. Nbcs chief foreign correspondent, richard engel, shows us the desperation inside aleppo. Reporter the Syrian Regime has been fighting rebels in aleppo for years now. But an air strike is clearing the way. First syrian troops are advancing and destroying the city in the process. Activists in the White Helmets dig through the rubble for survivors. They provided us with this footage to show the world what is happening in aleppo. One of the volunteers told us by skype that he fears the citys fall is near. We are so worried, because if we lose aleppo, we lose all the war. Changes the game . Yes. Absolutely. It changes everything. Reporter aiding, he says, 70,000 people already escaping aleppo in the last few weeks. Panic is spreading in aleppo that the regime plans to starve the city into submission. Its a tactic theyve used in other places. Thats why we are sending this to you and all the world. We need help. Reporter what kind of help do you need . What are you looking for . Now, we need just to stop the russians. Reporter the russians say they are bombing isis targets in aleppo, but ismael said thats just an excuse. We dont have any isis. They just helping the forces and killing us. Reporter the u. N. Said 300,000 people are still stranded inside aleppo and fears an unprecedented wave of refugees may be leaving the city in the next few days. Refugee crisis far worse. Richard engel, nbc news, new york. There is a lot more to tell you about tonight. Still ahead, new details about that nightmare cruise. Well hear firsthand from those onboard it. 30foot waves battered the ship. One newlywed said she feared she would die on her honeymoon. They could be the first astronauts on mars, and theres we are back now, with the passengers thankful to be back on dry land on what one called the cruise from hell. The ship rocked by a powerful storm with Hurricane Force winds and 30foot waves. Water rushing inside. Many wondering why the ship set sail with that storm coming in the first place. Heres the details. Reporter passengers describe it as terrifying. The chaotic hours, the anthem of the seas sailed into the middle of a massive storm. I thought im going to die. Drowning in the ocean. It was very scary. Reporter lee honeymoon. Kyle leveque was with his mom. Absolutely. I think 5,000 people lives were at risk. Reporter Royal Caribbean say the storm became worse than predicted. Two days before the cruise even started, the National Weather waves as high as 31 feet. In the same area anthem battled the storm. This was a system that was well forecast days in advance. There were even hurricane Wind Warnings out the day that the cruise ship left for the area where they hit the hurricaneforce winds. Reporter passengers say the ship felt like it was tilting side to side in Hurricane Force winds. Waves crashing as high as the fifth deck. Inside, passengers scrambled for cover amid shattered glass and flying furniture. One of the scariest day of my entire life. Reporter tonight the ntsb is part of the investigation into what happened, and the coast guard reports the ship needs more repairs before it can sail again. Royal caribbean said anthem is scheduled to cruise the same waters starting saturday, possibility of yet another storm. With the 4500 passengers getting refunds and credit toward a future cruise, few regret this vacation is over. Im grateful im reporter nbc news, new jersey. When we come back, its taken a century, but one of einsteins famous theories has finally been proven you dont see this every day, a congressman getting a nicotine fix right in the middle of a hearing. Duncan connor took a puff off a vaporizer to protest a measure that would ban it on planes. He said theres nothing toxic about the vapor. The congresswoman next to him waving it away didnt seem to appreciate it. Titanic is getting a sequel. Its debut is being pushed back from this year to 2018. An australian tycoon commissioned a replica over a century after the original sank. The new one is said to have upgrades including more lifeboats. A major announcement today confirming something einstein predicted a century ago. Scientists have detected navigational waves rippling across the universe, when two black holes collide to form one. Think of it like the Ripple Effect of spreading water when except these collisions so monstrous they can shake the fabric of spacetime. Its a very big deal, or so ive been deal. When we come back, suiting up with nasas next generation. Could become the First Americans to set foot finally tonight, a help wanted sign of sorts, getting an astronomical number of applicants. Nasa is hiring its next generation of astronauts, the first new class in four years. And some could ultimately be bound for mars. Nbcs tom costello has more from Johnson Space center in houston. Reporter for theyve been americas heroes. Thats one small for man reporter the men and women with the right stuff. Now nasas next up. Jessica mei, ph. D. In astronaut class of 2013. In your dream world, do you think about what kind of a mission you would love . I think i would like to go back to the moon. That would be a great first step. Shes in the water training for a mission to the space station. Its one of the biggest indoor pools in the world, the equivalent of 60 olympic pools, deep enough to hold 6 million gallons of water, and every new astronaut will spend considerable time here getting wet. Im the first person to be alone on an entire planet. Reporter the movie martian, a real mars mission could be 20 years away. The next class of astronauts, minimum requirements, a bachelors degree in math, science or engineering with experience or a military background. Communication skills, to be able to successfully work on a team, both a leader and follower. Reporter a mars mission could last two to three years. Would you want to go camping with somebody you cant get along with, spend a week in the woods with them, let alone two years in a tent with those people . Reporter nasa only astronauts, but already more than 6,100 people have applied online. Future missions could include a rendezvous with an asteroid, even we can send people there and bring them back safely, i would be up for it. Reporter two to three years, far from home, for some the stuff dreams are made of. News, houston. That will do it for us on this thursday night. Im lester holt. For all of us at nbc news, thanks for watching, and good announcer today on the Meredith Vieira show. But you will not believe the shocking confession kate made about her character. What we are obsessed with in time of valentines day. And Tiffani Thiessen is here dirk about her show. And adorable kids that shoot arrowses to your heart. It is the kids valentines day edition, all right now on meredith. Makes you feel real good. Feel real good. [applause] meredith hi, everybody. We have a great show today. We all fell in love with her on saved by the bell. Actress Tiffani Thiessen is here. She was pregnant and has had a little boy. I cant wait to hear about that. Plus, i know. To reveal the valentines day obsessions. First well talk about whats hot now. [applause] megan i have is the saved by the bell theme song. Show. She has an amazing cooking show. Meredith shes known you 20 years. Lance all of the skafinger hunt said you have to go to a 90210 home. Meredith she liked you . [applause] megan i would hope my door. Meredith since it is valentines day. You are obsessed by titanic. The wonderful story of rose and jack and how romantic. Get over it, she killed him. Kate winslett that that guy could have gotten on. There was enough room and she pushed him off. Lance he takes the blame. He tried to get on the piece of wood. Try a couple of more times. Megan he was frozen. Lilliana it is, on the aerial shot. Megan it is a big, big dor. But the water. In two seconds. Meredith he wasnt. Megan you have never seen titanic . Lance that is so unamerican