Nignightly news good evening. We begin tonight with what appears to be a turning point in this countrys relationship with iran. The u. S. Confirming late today that iran is complying with the agreement reached last summer on reducing its Nuclear Capability and that paved the way for the lifting of western sanctions against iran. It comes just hours after the regime released five american prisoners. The release of four of them, part of a prison swap. We start in vienna. Reporter good evening. The breakthrough was announced here and diplomats here are now calling in implementation day, the day the Iran Nuclear Deal comes into effect, the day iran was welcomed back to international markets. It seemed like a sweetener in a nuclear deal worth billions to iran, and for five americans, it was sweet indeed. They were finally freed. We have received confirmation that five americans who had been unjustly detained in iran have been released from custody. Among those released amir hekmati, a former marine held for over four long years, accused of aiding a hostile country. Saeed abedini, a christian pastor jailed for over three years. It seems like a dream. Reporter and Jason Rezaian held often in solitary confinement for a year and a half. Its spectacular news. Accountant wa cant wait to see him. Reporter the Washington Post in a statement said we couldnt be happier to hear the news. Matt trevithick, a student held for 40 days, was also released. While the prison swap is technically unrelated to the nuclear deal, critics had denounced washington for signing any agreement while teheran held americans. And hours after the swap was announced, the nuclear deal over two years in the making did move ahead. Iran has carried out all necessary measures under the agreement. Reporter the u. N. s Atomic EnergyAgency Certified that iran is keeping its word and has put checks on its program to make it far more difficult for iran to develop a nuclear weapon. The fact is today marks the first day of a safer world. Reporter so washington and the eu kept their word today dropping sanctions that have been crippling the iranian economy, giving iran access to World Markets and billions of dollars in frozen assets. We welcome that iran has followed through on the promises that it made. It has kept its word and we will continue to do the same. But we will also remain vigilant in verifying irans compliance every hour of every day in the years ahead. Reporter at least two americans are still either held or missing in iran. The americans released today are expected to eventually make their way to germany for medical checkups before heading home. Thank you for more on the Iran Nuclear Deal. We turn to our chief Foreign Affairs correspondent. Andrea mitchell. She is in South Carolina getting ready for tomorrow nights democratic debate. Reporter good evening. Well this prison swap and the implementation of the nuclear deal became a big issue in the campaign of 2016. Republican candidates led of course by donald trump pounced on the idea of releasing iranians from u. S. Jails to get the americans back. And even former secretary of state Hillary Clinton took a hard line. She released a statement tonight saying we shouldnt thank iran for fulfilling their nuclear obligations. She also pointed out that iran is still violating u. N. Resolutions against their missile program. U. S. Officials said they did not link the prisoner release to the nuclear deal because they didnt want the prisoners to become a bargaining chip in the nuclear that talks. The talks to release the prisoners did accelerate. One thing is very clear though. Iran was desperate to get out from underneath the nuclear sanctions, the economic sanctions, and back into the oil business. All the political noise tonight makes it clear that there are a lot of hurdles left before iran and the United States are going to restore full diplomatic relations or full business relations anytime soon. Thank you. By the way, thats where the Top Republicans were today and where the democrats will be tomorrow to square off. Reporter with the one time bromance between donald trump and ted cruz over, increasingly heated rhetoric. It seems donald trump has a lot of nervous energy. For whatever reason, donald doesnt react well when hes going down in the polls. He finally went off the wagon a little bit and went a little crazy. Reporter with the two locked in a tight race in iowa, both are escalating their attacks. Trump chastising cruzs suggestion that he embraces new yorks liber liberal attitude. You have people running up the stairs as that is happening and ted cruz criticizes new york and the people of new york is a disgrace. Reporter cruz not saying hes sorry for criticizing trumps values. In terms of a commander and chief, we ought to have someone who isnt springing out of bed to tweet in a frantic response to the latest polls. Reporter cruz even making an offhanded jab at trump after getting stuck in an elevator for about three minutes while campaigning in South Carolina. Who put donald trump in charge of the elevators . Reporter another showdown in the same southern state. The democrats squaring off tomorrow in their last debate before the iowa caucuses. Hillary clinton and Bernie Sanders off the trail today, but former president bill clinton making his wifes case in iowa. You just have to decide whether you want a change maker, not a change talker, to be president. Reporter while sanders is surging in the hawkeye state, questions remain about his ability to win more diverse states like here in South Carolina. The question, can he find a way to connect with more africanamerican voters. It wasnt enough for him to stand up and say i was with the Civil Rights Movement back in the 60s. You have to pay your dues again now because the landscape has changed and the issues have changed. Reporter an indication sanders is serious about reaching more diverse voters, hes putting up ads on africanamerican radio stations. Hes also holding a number of Campaign Events throughout the south, including here in South Carolina this weekend. Sanders and the other Democratic Candidates will try to court voters at a party dinner here tonight. Back to you. Lester holt will moderate tomorrow nights debate. He joins us now for a look at some of the key issues. Good to see you. Good evening. Andrea and myself have been involved in planning sessions all day, technical rehearsals getting ready for the debate. Its the last debate before the first votes are cast in this election. It also comes with the polls in iowa showing the two in a virtual dead heat. Its critical and we have seen it certainly in many of the attacks of the last week or so, especially Hillary Clinton going after Bernie Sanders on health care. His universal Health Care Plan which she has maintained will unravel obamacare. Also look for sharp clashes on gun control. Always a topic of contention between the two of them, but consider where we are in charleston where a man with a gun killed nine people in a racist shooting at a church here last summer. Thats critical. Finally, look for the issue of wall street to come up. The clinton folks in not happy about what they perceive to be as an attack that came out earlier in the week by the sanders folks referring to her relationships with wall street. It will play out on the stage behind me. You can watch the debate live tomorrow night at 9 00 p. M. Eastern time, 6 00 pacific right here on nbc. Chuck todd will interview Hillary Clinton and Bernie Sanders and marco rubio and jeb bush on meet the press. At least one american is among dozens killed in a terrorist attack on a hotel in west africa. The siege came to an end today when military forces killed several Al Qaedalinked extremists and freed more than 100 people. Our report tonight. Reporter it was dinner time when militants set fire to cars and started shooting inside this Splendid Hotel and cafe cappuccino across the street. She was at the cafe with her american friends. We played dead, she said. The shooters touched peoples feet to see if they were alive and would shoot if they moved. Reporter witnesses said it took hours for help to arrive. French special forces flown in from neighboring mali and a small group of u. S. Forces backed up troops as they cleared the fivestory hotel room by room. The militants still shooting as soldiers escorted people out. By dawn, it was over. Three militants dead. A fourth killed at a nearby hotel. The government said two of the militants were women. Among the injured and dead people from 18 different countries, including an american missionary. He and his wife amy worked with orphans for the Christian Charity sheltering wings. His family confirmed his death. His wife writing, heaven has gained a warrior. The state department wouldnt say whether more americans were killed or injured, only that our embassy is making every effort to account for u. S. Citizens in the city. Tonight the same Al Qaeda Group that assaulted a Radisson Blu Hotel in mali last november is claiming its followers carried out this attack calling it revenge against france and the disbelieving west. In hawaii, the second day of searching for a dozen u. S. Marines who were on two helicopters that collided off the coast of oahu. The search hampered by high waves. Reporter rescuers operating with urgency. 12 marines now lost at sea for more than 24 hours. Search teams at times facing 20 mile an hour winds and 16foot swells scouring an area 20 miles along the coast and 8 miles out. Military officials believe two ch53 helicopters were on a nighttime Training Mission three miles off the shore of oahu when they collided many midair. Went silent for a second and then all of a sudden two big booms. Reporter the crash so violent and unexpected no mayday calls were broadcast. But the explosion lit up the night sky. It was just a big fireball comes down. Reporter Officials Say each helicopter was manned by six service members. Tonight, their families are desperate for answers. Among the feared lost, major Shawn Campbell and Corporal Matthew drown both from houston. Christopher orlando an avid surfer from massachusetts. Captain kevin roach from missouri. Crew chief ty hart from oregon married just six months ago. I dont know anyone who wouldnt like ty, just a friendly person who seemed to be doing the right things and positive. Reporter tonight the navy and coast guard continue searching the oahu coast. Theyre walking the coastline, theyre walking the beach, just looking for anything and everything. Reporter and with debris scattered for miles and poor visibility, hope right now is fading. When nightly news continues this saturday, a federal emergency declared in flint, michigan, as that city struggles to deal with toxic lead in its water. Later, a long awaited debut at the national zoo. Weve got the bei bei pictures for you. thats lif song thats life song thats life song thats life thats life. You diet. You exercise. And if you still need help lowering your blood sugar. This is jardiance. 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Reporter the shred of good news for residents these days comes bottled and handed out at fire stations these days, a combination of federal and state help on the ground finally. Ive got a 3yearold. I dont want her to get sick. We keep paying taxes. We keep paying water bills. When does it end . Reporter the entire population roughly 100,000 was potentially exposed to lead. More than 9,000 children under the age of 6 and the water is still contaminated. We werent told the truth. You can hear the people. They have lost faith. Reporter even with escalating declarations of emergency. First by flints new mayor in december, then michigan Governor Rick Snyder last week. Today president obama declared a federal emergency. But this crisis began over a year ago silently when the city switched from a detroit water system to the flint river to save money. Nbc news obtained a 2011 study commissioned by the city that shows the river can be used if treated with multiple chemicals, but experts say the water was never treated. The way this was handled was just outrageously negligent and in some cases criminal. Reporter at the time, state Health Officials dismissed the findings. Can you come tomorrow at 10 00 . Reporter we met pastor Bobby Jackson last week. Were out of water right now. Reporter viewers donated generously, but more is needed. Those with the power to make massive change should be moving faster. Reporter now there is a federal criminal investigation. Long term flint will likely have to replace all of the old lead pipes. Clean tap water could be months, even years away. When we come back, well take you inside an oldfashioned Family Business that shapes the cars of the future. Ibsd. You know the symptoms when they start. Abdominal pain. Urgent diarrhea. Now theres prescription xifaxan. 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As any driver knows, todays new cars are marvels of technology loaded with advances that make them seem safer and easier to drive, but did you know in the process of getting there carmakers also use a technique that was developed long before computers were even invented. The key role of model cars. Reporter margaret and jim get into daily scrapes at work but it has nothing to do with their marriage. Theyre both clay modelers. Fell in love on the job. Spent years shaping the all new Lincoln Continental unveiled this week. Most people dont grasp the concept of what we do using clay as a medium and everything like that and doing fullsize vehicles out of clay. Reporter the craft of designing and building cars with clay, a painstaking laborious process, is nearly as old as the automobile itself. Rolls of clay warmed to make them pliable, those enticing curves and scoops and bends we want in our rides are chiselled and scored and smoothed to reality. The clay was used to refine these Little Details . Absolutely. Yeah, yeah. Reporter lincolns design director says there simply isnt a better way to get a vehicle off the drawing board or computer and on the road. You want to work on real scale, a 1 to 1 scale. There are things we can do digitally very quickly and easily, but really youve always got to test that. Reporter the interior is all about fine details like the seat stitching, control knobs, even the small speakers in the doors, everything is sculpted out of clay. Reporter they etched out their unique careers in large part because its a family tradition. Both their dads are modelers. Jims father retired. Margarets has graduated from a more 21st century version 40 years in. Its a cheap downpayment on a much bigger investment for automakers. We bought a fusion. I got in the car and im like this looks really familiar. Reporter one family and an entire industry firmly gripping an unbreakable mold. 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The 5monthold couldnt have cared less if he was the days biggest draw. He slept right through his debut. He sleeps about 90 of the day. Reporter of course that didnt stop the crowds from trying to catch a glimpse of his rol rolypoly perfection. From the day he was born, bei beis been a star. Weve been mesmerized. His first steps, a healthy checkup. How long lungs sound good and clear. Reporter the first ladies of two countries came together to gave bei bei his name. And in a way, the 23pound cub is carrying the weight of the world. The Panda Program an important diplomatic tie between washington and the u. S. Bei bei will stay in washington for four years and then be sent to china. Were breeding pandas here and then the next generation of pandas will hopefully start to go back into the wild. Reporter bei beis mission may be conservation, but for most its all about cuteness. While not everyone got the best view today, how could you not forgive this face . Thats nbc nightly news for this saturday. Thank you for the privilege of your time. For all of us here at nbc news, thanks for watching. Good night. Nbc sports, home of the 2016 rio olympics, nascar chase for the sprint cup playoffs. And sunday night football only on nbc. Welcome to football night in america, brought to you by Navy Federal Credit union. After a firstround bye, the nfc west champion cardinals are getting set for their postseason opener. They host the packers, who are trying to earn a repeat trip to the nfc championship game. I know, i will never forget how special it is to be part of a super bowl champion