Contest to pick president ial nominees. Each party has two frontrunners essentially tied. This is only the beginning, of course, of a process that lasts enter june, but these caucuses have never been more important. With three major candidates trying to turn the process outsidein trump, cruz and sanders, outsiders, testing establishment candidates, including clinton. We have a team of correspondents. First well go to Major Garrett with the republicans tonight. Major . Reporter scott, to win donald trump needs massive new turnout, thousands of voters participating statewide. Four years ago turnout was about 122,000. Ted cruz is betting everything here, his Massive Organization can withstand voter turnout up to 170,000, but beyond that, it is trumps game and trumps night. Good morning. Its the day weve been waiting for. Reporter before dawn, ken brolin woke up 130 ted cruz central central tears living in this apartment complexes known as camp cruz. We give this our all for one moredy and we can be proud of what we did here. He is real. Reporter cruz volunteers worked the phones all day sunday at the Campaign Headquarters outside des moines, part of the largest mobile disition effort of any g. O. P. Candidate. Cruz himself is in his 99th and final iowa county today and called the race a statistical tie. I got to tell you, this race right now is neck and neck. Its all about turnout. Reporter Donald Trump Holding a small but significant lead on cruz said he was nervous facing voters for the first time. Win, lose or draw, i love you folks all. I love you all. Reporter trump also warned iowa corn farmers who rely on federal ethanol subsidies that cruz is no friend. He will destroy your ethanol business 100 , 100 . Thanks for everything. Reporter marco rubio who is hoping a late surge will translater to a strong finish exhorted volunteers and took selfies. Were ready for whatever happens tonight. We feel positive about it. I ask everyone to go out and caucus, especially if youre supporting me. Were volunteers of ben carsons campaign. Reporter supporters of ben carson who has sagged in the polls knocked on doors in one last gasp of support. And rand paul met with dozens of his young volunteers. Were going to do very well. Were going to beat a lot of people in the race. I think there is a chance we can win. Reporter rubio could be the one to watch, scott. His crowds have grown by hundreds down the stretch, and a strong finish could be a spring board to New Hampshire, where other rivals for the socalled republican establishment vote, jeb bush, Chris Christie and general kasich, are already waiting. Pelley major, thanks. Now the last precaucus poll out today shows the democratic race between clinton and sanders a statistical dead heat. Clinton hopes to redeem her loss in iowa eight years ago. Nancy cordes is there. Nancy . Reporter scott, clinton came into iowa with all the advantages must be, stats, years of planning. Tonight we find out if it is enough to fend off a former underdog who, like her opponent eight years ago, has taken on an iowa with a message about change. I really appreciate all your help. Reporter there was nothing left to do today but thank supporters. Let me thank not only all the volunteers. Reporter the phone calls have all been made. Would you be able to come . Reporter the doors have all been knocked on. I will be caucusing tomorrow. For bernie . Bernie, yes. Excellent. Reporter and no one has any idea who will come out on top. We got a tie ballgame. Reporter vermont senator Bernie Sanders has closed a 40point gap in six months. The adrenaline is flowing, yes. Reporter win or lose, he has pierced clintons aura of inevitability. What was the point that you thought, i could really be a contender here . Well, when we started to bring out really, really large turnouts, you know, in des moines and iowa city and people said, you know, bernie, for iowa thats a really, really big turnout. Reporter clinton, by necessity or design, has done smaller events. How many people here have already made a phone call or knocked on a door . Reporter making more time for the kind of personal interaction iowans see as a birth right. The candidates closing arguments could not be more different. Stick with me. Stick with the plan. Stick with experience. It sounds like you want to make a political revolution. Reporter their faceoff has left former Maryland GovernorMartin Omalley a distant third. If you dont change the dynamic here, what happens in New Hampshire . We. Look, you have to ask me that after monday night. Reporter clinton could survive a loss here in iowa, but it wouldnt be much fun. Sanders is leaving in his neighboring state of New Hampshire by as much as 20 points in the polls, and if he win, scott, clinton wont have chance to redeem herself until South Carolina at the end of the month. Pelley nancy, thank you. Its worth remembering that only 30 delegates are at stake the tonight. It takes many hundreds to win either partys nomination. John dickerson is our cbs news political director and anchor of face the nation. Hes in iowa talking to iowans. John, iowas conservatives are about as conservative as they come. Tailormade for cruz. What if he comes in second . It would be a blow. His campaign is always predicated on starting and doing well in iowa. That is because its tailormade for him there. There are so many evangelical voters here and conservative voters. His entire campaign is built around this idea that he can build a conservative revolution. If he cant do that here, it calls the whole thing enter question. But he has about 20 million cash on hand, and there are future contests in South Carolina and then a number of Southern States on first of march that would do well for him, so if he comes in second here, he could mount a comeback in those states. Pelley it also seems that iowas liberals are tailormade for sanders. Hell do well in New Hampshire next to his home state next week, but what about the later primaries for sanders . Reporter those laters primaries, the lech track is less liberal. Hillary clinton has Better Organization in those states, so its harder for sanders to build the kind of emotional support and wave that hes trying to build here in iowa. Thats why iowa is so important. Because if he cant do it here, hes not going to be able to do it in later states. Pelley majorc was just telling us mainstream republicans are fighting for third place. Why does that matter . Reporter well, those mainstream republicans, and here were talking about rubio, bush, christie, kasich, theyve been trying the find some reason to break out of the pack and say i am the lone alternative to donald trump and ted cruz. So theyve grabbed a poll. Theyve talked about a debate performance. Nothing has allowed them to broke out of the pack. If they can point to a strong result in iowa, third or maybe second, they can say the voters have validated me and now all mainstream conservatives should rally around me to go up against trump and cruz. Pelley john dickerson, see you on face the nation, thanks, john. Now, we are thrilled to welcome back to the evening news man who has covered every president ial election since 1968, our very own bob schieffer. Bob, how does this one look to you . Reporter thank you, scott. I have to say, primary campaigns are like weddings, they bring out the best and worst in families. If this campaign were a wedding, we would be halfway through the weird uncles long, unfunny and embarrassing rehearsal dinner toast. The difference here is all the participants in this campaign appear to be stonecold sober. That may be the scariest part of all. People are madder than ever, the partisan divide is wider than ever, and were seeing a campaign reflecting the changes in our culture brought on by social media. Nasty, illogical, illtempered, strong on attitude, light on issues. Too many times people have arrived at this wedding with not just opinions, but their own set of facts. The Campaign Narrative has gone in inane to profane, more like a thread on a blog post than the usual campaign rhetoric. Youre a jerk. Well, youre a bigger jerk. No, youre a blank, blank jerk. Inspirational . Not just yet. But there is light at the end of the church. In iowa tonight, as the candidates finally begin their long walk down the aisle of the caucus and primaries, well finally start the hear from another group voters. Scott, thats a good thing. Drew . Pelley and youll be with us on the long walk to ewill election day. Bob, thank you. We will have updates for you tonight on the caucuses during prime time programming. Stick with us right here on cbs. And cbs thursday cbs this morning will have tomorrow. Snow is on the way tonight in iowa, but not until after the caucuses. California got hammered by weather the past two days, and san diego and eightfootwide oak fell on a car and killed a woman. Wind gusts were reported as high as 115mph. To the north i80 was shut after a pileup of 29 vehicles. This system could dump a foot of snow on denver. In another major story tonight, the World Health Organization took the rare step today of declaring zika virus and its suspected link to severe birth defects and International Public health emergency. The outbreak started in brazil and our doctor jon lapook is there tonight. Jon . Reporter scott, i spent the day at this hospital, which has seen the most number of cases of microcephaly in all of brazil. The couple i spoke to was anguished as they tried to figure out what this condition means for their baby. Alice Bezerra Depaz had a healthy first baby, but two months ago her second child, joao heitor, was born with microcephaly, a birth defect linked to the zika outbreak. Babies with microcephaly have an unusually small head and developmental delays. We never expected to have an infant like this, she said, but we will care for him the same way. Today the parents came to the oswaldo cruz hospital where doctors have seen about 300 infants with microcephaly since september. Before that this region only saw an average of nine cases a year. Dr. Angela rocha heads up the effort here to understand and manage the crisis. In her four decades as a pediatric Infectious Diseases expert, she has never seen anything like it. This is different, she said. Its a generation of babies with disabilities, which is a huge social, economic and Public Health problem. Tell me what its like to have a conversation with a mother and tell her that her baby has microcephaly. Its a situation with a lot of stress, panic, worry and insecurity, she told me. Thats because these parents and even Health Experts here are trying to figure out what services these infants will need. Today the president of brazil gave Public Health officials the right to enter any home or business to try to eradicate mosquito breeding grounds. Scott, well be reporting on this in the dame to come. Pelley jon lapook in brazil for us tonight. Jon, thank you. Amtrak is trying to figure out what hit a highspeed acela train last night in philadelphia. Whatever it was, it gashed a window and the train was taken out of service. Nobody was hurt. This is eerily similar, though, to last may when a commuter train was hit by something just before an amtrak regional train crashed in philadelphia. That crash killed eight and injured nearly 200. And today federal investigators gave us an update on their investigation. Heres kris van cleave. Reporter newly released pictures taken from train 188s dash cam a show the moment the speeding train left the tracks. Engineer Brandon Bostian told investigators about a minute before the accident he realized he was going ten miles too slow and began accelerating. His next memory was feeling as though i was going too fast around a curve. The trains event recorder found bostian applied full throttle oy approximately a mile and a half from the curve. The train reached 106mph before bostian hit the emergency brakes. He said, i remember holding on to the controls tightly and feeling like, okay, well, this is it, im going over. Toxicology reports found no evidence of drugs or alcohol in bostians blood, and he was in the using his cell phone at the time of the crash. Lawyer tom kline represents several of the hundreds who were injured. The train was being operated at 106mph and there was a system that could have been in place and in fact was in place going the other way on the tracks which could have prevented it. Reporter that technology, positive train control or p. T. C. , is now active along amtraks heavily used northeast corridor linking boston to washington, d. C. Im going to try and put full power on the train here and see how fast i can do. Reporter amtraks chris jagodzinki showed us how p. T. C. Prevents a train from going too fast. Now, what happened here is this. Traction blocked. Its taken away all the power in the locomotive. Now its applying the brakes. Reporter so regardless of what you do. I cant do anything. The computer has taken over. Reporter investigators found no issues with the train, the tracks or the signals. Scott, we still dont know definitively if and when an object may have struck the trains windshield and if that could have contributed to the crash. A lawyer for bostian declined to comment. Pelley at 106, that was double the speed limit on that curve. Kris, thanks very much. One of the super bowl quarterbacks addresses a report that he used a banned substance. And danger on the high seas when the cbs evening news continues. And those in megared krill oil. Unlike fish oil, megared is easily absorbed by your body. Which makes your heart, well, megahappy. Happier still, megared is proven to increase omega3 levels in 30 days. Megared. The difference is easy to absorb. Does your mouth often feel dry . Multiple medications, a dry mouth can be a side effect of many medications. But it can also lead to tooth decay and bad breath. Thats why theres biotene, available as an oral rinse, toothpaste, spray or gel. 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You have vehemently denied the allegations with h. G. H. Right. I know the nfl is doing an ongoing investigation. Have you talked to them and do you plan on fully cooperating with them . Absolutely. And as far as i know, thats going to start after the season as far as my role. And i welcome that investigation. And i understand when an allegation is made that the nfl has no choice to investigate it. I get that. But i can tell you what theyre going to find, a big fat nothing. Its been completely fabricated as far as the allegations of what they suggested that i did. Its been nothing but pure junk, and i welcome that investigation. So i think that will start right after the season. The quarterback on the other side on sunday, cam newton, describe his style . Oh, boy, hes fun to watch. Do you know that last week his longest run was 14 yards and yours was 12 . The difference is it took him, you know, 1. 2 seconds the make 14 yards. It took me ten seconds to get 12 yards. You had the use the clock. Im glad you pointed that out. It sure felt like i ran a lot longer. It fell like a 30yard run. I only got 12 . Pelley you can see the interviews with Peyton Manning and the panthers cam newton this sunday on cbs during coverage of super bowl 50. The pregame begins at 2 00 eastern. Theres an update on the e. Coli outbreak traced to chipotle restaurants. Thats ahead. When i was sidelined with blood clots in my lung,h. It was serious. Fortunately, my doctor had a game plan. Treatment with xarelto®. Hey guys hey, finally, somebody i can look up to. Besides arnie. Xarelto® is proven to treat and help reduce the risk of dvt and pe blood clots. Xarelto® is also proven to reduce the risk of stroke in people with afib, not caused by a heart valve problem. For people with afib currently well managed on warfarin, theres limited information on how xarelto® and warfarin compare in reducing the risk of stroke. 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Coli bacteria linked to chipotle. Now the government says there hasnt been a new case in two months. And this cargo shiploaded with wood, Construction Equipment and fuel started listing off of france. Rescuers couldnt reach it for five days because of the weather, but today they towed her to safety. In a moment the opening shots in the battle for the white house. This is my body of proof that i can fight Psoriatic Arthritis with humira. Humira works by targeting and helping to block a specific source of inflammation that contributes to both joint and skin symptoms. Its proven to help relieve pain, stop further joint damage and clear skin in many adults. Doctors have been prescribing humira for 10 years. Humira can lower your ability to fight infections, including tuberculosis. Serious, sometimes fatal infections and cancers, including lymphoma, have happened, as have blood, liver and nervous system problems, serious allergic reactions, and new or worsening heart failure. 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Theres john kerry on the floor and the bench, al haig with a pig let, john mccain, back and front, two marco rubios and two joe bidens 20 years apart, bushes father and son and son, and the clintons, then and now. The thing about iowa is it can really make a candidate. It can bring somebody like jimmy carter to National Prominence or even obama when he was here. And with dean it was the opposite. It sort of doomed his campaign. Reporter this is your picture . This is my picture. Reporter former Des Moines Register photographer doug wells captured howard dean hitting the highest note at his lowest point. And then were going the washington, d. C. , the take back the white house. Yeah reporter today wells is the curator of this exhibit. We started shooting. We knew something was different. We knew something was happening. Reporter he didnt ask for a copy of this picture, did he . Not that i know of. Reporter Mike Huckabee visits a barbershop and jams with the king. Michelle bachmann holds a side of beef. I think we were wondering why she decided to visit the meat locker. Reporter there are protests and arrests, and a flag is here in abundance. Mitt romney the candidate always seemed freshly pressed, and on caucus night four years ago, so was thing from at his premature victory rally. Photographer Christopher Gannon spotted it. This gentleman came out and plugged in an iron, and im thinking to myself, what is going on here. Reporter its a question you can ask about a lot of these amazing photos, and one of the great things about the caucus is that there will be many more to come. Dean reynolds, cbs news, des moines. Pelley and thats the cbs evening news for tonight. Well be back with updates on the Iowa Caucuses beginning at 8 00 eastern, 7 00 central. For all of us at cbs news all around the world, im scott pelley. Well see you again soon. 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