>> 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 mid-winter. even though we are just an hour ahead of u.s. eastern time, the sun think february in the states without the cold. we'll 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 nine-point lead over donald trump. 47% to 38%. that's up from a five-point 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 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, what's going on here? >> reporter: but straying again claiming he saw video of iranians offloading that cash. >> that was given to us the iranians. you know why the tape was given to us? because they want to embarrass our country. >> reporter: the problem? there's 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. 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 wife's history was bound to get scrutiny. >> repor a 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 don't. >> reporter: the trump campaign is insisting that they are getting back on message. this as new battleground polling is showing what's at stake. trump is down double digits in pennsylvania. 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 administration's isis strategy, president obama once again 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 trump's repeated assertions the election will be rigged. >> that's ridiculous. that doesn't make any sense. and i don't think anybody would take that seriously. >> reporter: and he handed down a stunning warning when asked about trump receiving intelligence briefings which both candidates 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 toet financial dispute. >> we do not pay ransom for hostages. >> reporter: kristen welker, nbc news, the white house. we're 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. nbc's kelly cobiella has more from london. >> reporter: flowers on a central london state university 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: 64-year-old horton died on this sidewalk. tonight fsu's 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 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. 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 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 women were told today no testing here, try another office. >> i'm 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. to for failing to fund zika before taking a seven-week 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 sure those mosquitoes don't bite people who then spread the virus elsewhere. kerry sanders, nbc news, miami. let's turn now to news breaking here in rio. the international olympic committee just announced how many russian athletes will be allowed to compete. a third of the country's 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 forc 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 haven't ever competed against somebody who spirit of sports. >> reporter: while rio is iconic for its incredible views, tonight what's 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. 292 of them are women. 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 women's soccer team's 2-0 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 gold than american men. women's 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 didn't think we'd see michael phelps here. >> no. he said he was done in london. he already won 22 olympic medals. 18 of them his he's got a chance -- he's got a very legitimate chance of taking on maybe three more goals. >> reporter: and don't forget the splash american katie ledecky made four years ago. >> she comes into london as a 15-year-old, 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. this kid. she's got real heft to what she does. and she does things that nobody else has ever seen before. >> reporter: and mary says don't count out jamaican sprinter usain both bolt. >> he's as big a presence as anyone. >> reporter: this is olympics 13 for mary who has extra reason to love the rio games. >> i've been watching so much television, so much political fighting and you hear the candidates saying this is what america american flag is going to go up for the next 17 days and people have relief from all that political fatigue. i don't have to tell you what that's been like. >> reporter: can i hug you and say mary carillo for president? that's my endorsement. mary carillo of nbc olympics with some pretty great perspective there. ahead of tomorrow's 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 the potential problem what if one piece of kale could protect you from diabetes? what if one sit-up could prevent heart disease? one. wishful thinking, right? but there is one step you can take to help prevent another serious disease. pneumococcal pneumonia. if you are 50 or older, one dose of the prevnar 13? vaccine can help protect you from pneumococcal pneumonia, an illness that can cause coughing, chest pain, difficulty breathing, and may even put you in the hospital. prevnar 13? is used in adults 50 and older to help prevent infections from 13 strains of the bacteria that cause pneumococcal pneumonia. you should not receive prevnar 13? if you have had a severe allergic reaction to the vaccine or its ingredients. if you have a weakened immune system, you may have a lower response to the vaccine. common side effects were pain, redness or swelling at the injection site, limited arm movement, fatigue, headache, muscle or joint pain, less appetite, chills, or rash. get this one done. ask your doctor or pharmacist after a long day, dave stops working, but his aleve doesn't. because aleve can last 4 hours longer than tylenol 8 hour. when people ask me what it's like to win an olympic medal, i tell them, "you already know." the medals you've earned are all around you. your bronze. your silver. your gold. and liberty mutual insures them all. liberty mutual is proud to insure every team usa medal won in rio, just like we protect the medals you've earned in life. back now from rio de janeiro. in the run-up to these games, doping has loomed large. there have been numerous athletes and national teams under the glare of the spotlight. tonight we're taking an ideas look at the u.s. anti-doping agency and why its chief believes usada is the best in the world at detecting cheaters and working american athletes are the cleanest. here's nbc's 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. anti-doping agency or usada is on a mission to make sure american athletes games, a doping scandal. russia's 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 we've ever seen. >> reporter: here in the u.s., athletes are tested at competitions and away from their sport. it's 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 don't 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 crossed and i's 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 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 we're 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. international olympic committee said 10,000 tests will be administered and they're 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 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now 31, the swimmer is a different person than the one we've come to know. >> i'm a lot more laid back, i'm a lot more relaxed, i'm a lot more open. >> reporter: his cheering section is different too. phelps' sisters and mother who've been staples in the stands are now joined by his fiance and their son boomer robert phelps. >> phelps is going to win it. >> reporter: at 2 months old, boomer saw his son compete for the first time. >> looked like boomer which was good. >> reporter: and qualify for his olympics. >> having my first born be there to watch is something that's special. >> reporter: boomer's middle name is in honor of his coach he's trained with since he was 11. he's like a completely different person. >> absolutely. in all the areas. it's all about the swimming now. >> reporter: that wasn't the case going into london. >> leading into london, i didn't want anything to do with phelps hated swimming. and often wouldn't show up to practice. but he and bowman put on a good front keeping their strained relationship hidden. prior to london, bob, was there a time you didn't think he was going to go? >> yes. >> reporter: you thought he was going to quit? >> i hoped he would. >> reporter: why? >> i thought it was going to end badly. >> reporter: it all came to a head in 2014 when phelps got arrested for his second dui and went to rehab. another day. i felt like it should be over. >> reporter: so did you check yourself into treatment because you had a drinking problem or because you had a public relations problem? >> i checked myself in because i think i was at a point in my life where something needed to change. >> reporter: he's sober now and there's a sense of self-acceptance. >> ready? go! >> reporter: people close to phelps says he hates to lose more than he loves to win so out of rio, what's realistic? >> there's a number in my head. don't hit the number, will you be able to look at me and say i went out the way i wanted to go out? >> yeah. because i'm giving an honest effort. i'm having fun again. and this is something that i haven't had in a really long time. >> reporter: there's no question he's always had that competitive fire. but this time he also has the passion. matt lauer, nbc news, rio. and that is going to do it for us on this thursday night from rio, our home for glad to be here. i'm lester holt. for all of us fios is not cable. we're wired differently, which means we can fix things differently. thanks for calling fios. this is ryan. you can't tell me this cord isn't in. i know it's in. it's in, but it's not working. i'm sending you a link to the my fios app that going to let me see what you're seeing. really? yes, mr. mcenroe... see that cord? just plug it into the connector on the right. so you can clearly see what's in and what's out? oh absolutely. i like that. only from fios. camera. access. >> as modern families go, how is your family doing? >> we are definitely a modern family. >> are jennifer garner exclusive. how she and ben are getting it done. i'm natalie morales. it's not the only part of jen's life that's wki >> oh, my gosh, it is so much better, natalie. >> i'll say this just in case of a comeback. >> is it possible michael phelps could go for not one but two more olympics after rio? i'm billy bush. and was it something she said? hope solo's less than warm welcome to the games. kris jenner's close call. with the accident that destroyed her rolls-royce and which family