Announcer this is nbc nightly news with lester holt reporting tonight from the olympic summer games in rio. Good evening from copacabana beach, one of the many competition sites for the games starting tomorrow here in rio. In this half of the world, it is midwinter. Even though we are just an hour ahead of u. S. Eastern time, the sun has been down here for some time. Think february in the states without the cold. Well have much more on the upcoming competition here later. But we want to start with a snapshot of the race for president. A new nbc news wall street journal poll shows that Hillary Clinton has opened up a ninepoint lead over donald trump. 47 to 38 . Thats up from a fivepoint lead just before the republican convention. And comes as the Trump Campaign struggles again to regain its focus after a blurring series of controversies. The latest one now involving his wife. Nbcs katy tur has details. Reporter tonight after his toughest week yet, donald trump is trying to turn the page. Training on president obama over a 400 million settlement payment to iran. 400 million being flown to iran. I mean, folks, whats going on here . Reporter but straying again claiming he saw video of iranians offloading that cash. That was given to us has to be by the iranians. You know why the tape was given to us . Because they want to embarrass our country. Reporter the problem . Theres no evidence that tape exists. Trump repeated his version even after his Campaign Said he was talking about generic footage of the detainees landing in switzerland. Now a new report concerning the timeline around when Melania Trump emigrated to the u. S. When she was a model and whether it was league for her to work here. Newly recovered photos place her in the usa in 1995, a year before she and trump say she first arrived. Melania telling msnbc in february i never thought to stay here without papers. I had visa. Reporter tonight firing back blasting inaccurate reporting and misinformation saying she was always in full compliance with immigration laws. Political spouses are normally off limits but in this case trump has made such a big issue of immigration, his wifes history was bound to get scrutiny. Reporter all of it coming as aides, confidants, and supporters are pleading with trump to get back to basics. Are the controversies wearing on you . Yes, they are. But not as much as they are my wife. He has a good message to tell and the democrats dont. Reporter the Trump Campaign is insisting that they are getting back on message. This as new battleground polling is showing whats at stake. Trump is down double digits in pennsylvania. Lester . Katy tur in maine, thank you. And for his part, president obama said today that while donald trump needed to receive Intelligence Briefings as a candidate, a candidate also needed to act like a president and not spread those briefings around. The president also spent a great deal of time talking about the fight against isis. We get more tonight from kristen welker. Reporter in a press conference at the pentagon designed to tout the obama administrations isis strategy, president obama once again jumped into the 2016 race targeting donald trump. I obviously have a very strong opinion about the two candidates who are running here. One is very positive and one is not so much. Reporter the president today asked about trumps repeated assertions the election will be rigged. Thats ridiculous. That doesnt make any sense. And i dont think anybody would take that seriously. Reporter and he handed down a stunning warning when asked about trump receiving Intelligence Briefings which both candidates are now cleared for by law. If they want to be present, they got to start acting like president. Reporter but donald trump and republicans have also put the president on defense accusing his administration of paying ransom for americans held in iran after revelations the u. S. Sent a 400 million cash payment to iran in january coinciding with the release of those americans. We have a president who frankly is incompetent. Reporter the president firing back at his critics arguing the cash was to settle a decades old financial dispute. We do not pay ransom for hostages. Reporter kristen welker, nbc news, the white house. Were learning more about a horrific attack on the streets of london. A stabbing spree that claimed the life of an American Woman from florida leaving five others injured. Investigators say there does not appear to be a terror connection. Nbcs Kelly Cobiella has more from london. Reporter flowers on a Central London sidewalk for darlene horton. The wife of a Florida StateUniversity Professor stabbed in the back. A witness who took this picture said paramedics tried for 20 minutes to save her. You could just see they were applying a form of cpr. Reporter 64yearold horton died on this sidewalk. Tonight fsus president said there are no words to express our heart ache. Her husband Richard Wagner was teaching in london for the summer. It was their last night in the city. The couple due to fly home to tallahassee today. The man injuring five others in a stabbing spree. Shown in the video on the ground being restrained was mentally unstable. No ties to terrorism, no sign of radicalization, police said. At this time we believe this is a spontaneous attack and that the victims were selected at random. Reporter the city already on alert for terrorism. You said it was chaos. It was chaos. Because nobody knew what was going on. Reporter tonight praise for the action of police on scene in just six minutes. The suspect quickly spotted, tased, and restrained. Sadly too late for a florida family now grieving for a wife and mother. Kelly cobiella, nbc news, london. As miami deals with a home grown zika outbreak, the cdc said today that more than 1800 americans have now been diagnosed with the virus after catching it overseas. Including 479 pregnant women. At his news conference, president obama sharply criticized congress for going on recess before authorizing more funding to fight zika. Meanwhile in florida, concern remains high about how far the spread of the virus may go. Kerry sanders has the latest. Reporter pregnant mothers to be in florida have been promised free zika tests. Yolan baptist among the lucky first. Women were told today no testing here, try another office. Im concerned, yes. Because this is my first pregnancy and i want it to be a successful one. Reporter rather than wait for the state, Tracy Humphries went to quest diagnostics, a private lab for testing. Her husband did too. If i do see mosquitoes and i think i have any bites, i would get tested again. Reporter zika test results take two to seven days and in many cases may have to be repeated. Today president obama criticized congress for failing to fund zika before taking a sevenweek vacation. Zika is a serious threat to americans. Especially babies. Right now. So once again i want to urge the American People to call their members of congress and tell them to do their job. Reporter some good news today. Two days now and no more home grown zika cases. The cdc here today clarified the area where the zika mosquitoes are could be as small as 500 square feet. The challenge, making sure those mosquitoes dont bite people who then spread the virus elsewhere. Kerry sanders, nbc news, miami. Lets turn now to news breaking here in rio. The International OlympicCommittee Just announced how many russian athletes will be allowed to compete. A third of the countrys team has been banned after a major doping scandal. It comes on the eve of Opening Ceremony as this city remains cloaked over a massive security force. The largest ever deployed in brazil. Miguel almaguer is with athletes and the military. Reporter tonight for team russia in rio, a split decision for many athletes appealing a ban after a widespread doping scandal. The message is clear. No place to hide for cheats. Reporter boxers and many members of the swim team given the all clear to compete late today. I think i would be naive to think i havent ever competed against somebody who has done something that was against the spirit of sports. Reporter while rio is iconic for its incredible views, tonight whats most stunning here is security. At the foot of christ, heavily armed soldiers. Even along the sands of copacabana, Police Looking for threats big and small. Robbery is the biggest concern down here . Yes. Reporter security remains tight along the olympic torch route. After days of protest, today few problems in this city of sand and surf. The torch one wave closer to the cauldron as tonight the world watches rio. Just 24 hours until opening ceremonies. We expect half a Million People to flood beaches like the one behind us here as well as this entire city. Lester, with this doping scandal, another layer of drama before the games get under way. The big sporting events, the most exciting ones are days away. Here we are. Thank you very much. The u. S. Is represented by 554 athletes here in rio. 292 of them are women. B the most women who have competed for any country. When we look at the athletes to watch, it is the american women leading the way. The usa womens soccer teams 20 win over new zealand yesterday sets them on the right path to clinch their fourth gold medal. And continues the dominance of american women. In london more american women won gold than american men. Womens basketball, they dominate. The williams sisters, they both won four gold medals. They can both win in singles and doubles. Reporter i met up with mary carillo to talk about which athletes could make big headlines here. Individually, behind us is the swimming venue. We didnt think wed see Michael Phelps here. No. He said he was done in london. He already won 22 olympic medals. 18 of them his favorite color, gold. Now hes come back and hes got a chance hes got a very legitimate chance of taking on maybe three more goals. Reporter and dont forget the splash american Katie Ledecky made four years ago. She comes into london as a 15yearold, wins the 800 free style, stuns the world. The future of usa swimming. Reporter four years later, she would win a fist full of gold. She wins by jaw breaking margins. Reporter in gymnastics, mary says watchout for simone biles. Im telling you, this kid. Shes got real heft to what she does. And she does things that nobody else has ever seen before. Reporter and mary says dont count out jamaican sprinter usain both bolt. Hes as big a presence as anyone. Reporter this is olympics 13 for mary who has extra reason to love the rio games. Ive been watching so much television, so much political fighting and you hear the candidates saying this is what america represents. I love the idea the American Flag is going to go up for the next 17 days and people have relief from all that political fatigue. I dont have to tell you what thats been like. Reporter can i hug you and say mary carillo for president . Thats my endorsement. Mary carillo of nbc olympics with some pretty great perspective there. Ahead of tomorrows official opening of the summer games. Still ahead tonight, making sure u. S. Olympic athletes stay clean. Our exclusive look at a surprise drug test being carried out. Also why ford has issued a huge recall. The potential problem what if one piece of kale could protect you from diabetes . 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Antidoping agency and why its chief believes usada is the best in the world at detecting cheaters and working to ensure that american athletes are the cleanest. Heres nbcs ron mott. Is there any stopping Lance Armstrong . Reporter the old adage cheaters never win has been debunked time and again in sports. They do win and sometimes get caught. The win at all costs culture is across the globe. Reporter head of the u. S. Antidoping agency or usada is on a mission to make sure american athletes never use drugs to cheat. Looming over the rio games, a doping scandal. Russias entire weight lifting team and all but one track and field athlete banned. The pressure on athletes to do whatever it takes to stop at nothing in order to achieve success is as great as weve ever seen. Reporter here in the u. S. , athletes are tested at competitions and away from their sport. Its a system bolstered by the element of surprise. Nbc news is with a doping control officer who showed up unannounced at 7 00 a. M. For a sample. We dont want the athlete to be prepared. Reporter the marathoner answered the door. His 115th usada drug test had just begun. You got nothing to worry about. Reporter at the olympic trials, after just making the team, a usada official never losing sight of him for nearly an hour until the sample was obtained. They make it really easy on the athletes but they also make sure all their ts are crossed and is are dotted. Reporter of the thousands of american athletes tested by usada each year, dozens are sanctioned. More than 120 since 2013. Sprinter Justin Gatlin failed a 2006 drug test and served a reduced penalty in exchange for cooperating. Tyson gay was also denied knowingly taking a banned substance. Both competing in rio. Though his number one priority is leveling the playing field. Obviously we have to hold individual athletes who cheat accountable. But getting to the root cause, the system of the win at all costs, those are the Leaders Within the sport. Team doctors, trainers, owners who may be pressuring athletes. Those are the ones were going our best to hold accountable. Reporter obviously there will be a lot of eyes and attention on the russians allowed to compete in rio. Today the head of the International OlympicCommittee Said 10,000 tests will be administered and theyre going to keep them on file for ten years for reanalysis. All right. Ron mott tonight, thank you. When we come back, charges of extortion, when we come back, charges of extortion, fraud, and even worse if you have moderate to severe plaque psoriasis, isnt it time to let the real you shine through . Introducing Otezla Apremilast . Otezla is not an injection or a cream. Its a pill that treats plaque psoriasis differently. With otezla, 75 clearer skin is achievable after just 4 months, with reduced redness, thickness, and scaliness of plaques. 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