for president may be feeling more and more like a reality show tonight starring a man who before he became a candidate, proved he could draw an audience. and so donald trump will likely have a lot of eyeballs watching tonight.t. either the republican debate that he has now vowed to boycott or his own event that could steal the spotlight. leading up to all this, a public dual with fox news, public pleas that he reconsider, even prime time discussions of milkshakes, all just four days until the vote in iowa. peter alexander explains. >> reporter: tonight should be the republicans final showdown before the wow caucuses. the front-runner staging his own prime time event to raise money for veterans. going head to head on tv with the fox news debate just three miles away. even drawing a pair of his underdog opponents. mike huckabee and rick santorum. >> by walking away from this debate -- i was pushed away. i'm not walking away. >> trump is defiantly positioning himself as the deal maker in chief. >> it's called an eye for an eye. >> i bought you so many vanilla milkshakes, you owe me. >> now >>. >> reporter: today, the billionaire launched this fundraising website, claiming 100% of donations to donald j. trump foundation will help vets. canines for warriors tells nbc news the campaign contacted them late today saying they're 1 of 18 nonprofits now under consideration. but a separate veterans group is skeptical, tweeting, money doesn't need to be funneled through a political campaign. just donate directly to groups doing good work. will trump's debate boycott backfire? his opponents say yes. >> it's not that he's afraid of me. he's afraid of you. >> reporter: still, trump has momentum and now the lead here in iowa. according to the >> what are the risks for donald trump? >> the risks for trump is that he looks weak by not confronting his opponents. the up side is he avoids being the pinata at the republican debate. >> reporter: marco rubio rising in the polls, already taking a swing. >> interesting side show. greatest show on earth. this is not a show. this is serious. >> reporter: late tonight, another twist. donald trump's campaign confirms to nbc news that trump would be willing to debate ted cruz one-on-one just as soon as the canadian-born senator gets a federal judge to rule on his el jib illity to be president. lester. >> thank you. on the democratic side of the race, our brand new poll shows hillary clinton and bernie sanders locked in a virtual tie in iowa even as the two campaigns look beyond the hawkeye state, debating whether to hold more debates. meantime, clinton is also getting drawn away from the trail to was quick to pounce on. we get details from nbc's andrea mitchell. >> reporter: it's a dead heat for the democrats in iowa. our new nbc news/"wall street journal" poll has hillary clinton leading bernie sanders by just three points, within the margin of error. but in sanders' neighboring new hampshire, the vermont senator has a commanding 19-point lead. with the race more competitive, beth are now agreeing to more debates, including next week in new hampshire if the democratic party approves. >> the political world has changed a little bit and now it seems like hillary clinton would like another debate. you know what? i said that's fine. i don't mind that. >> reporter: but facing a longer than expected primary contest, clinton left iowa wednesday afternoon to raise money in philadelphia from an investment firm and in new york today. >> some of my supporters, including my good friend john bon jovi had a fundraiser for me. >> reporter: but clinton's fundraising plays into one of sanders' top issues, 9 focus of a new sanders ad violates his pledge not to go negative. >> how does wall street get away with it? millions in campaign contributions and speaking fees. >> why isn't that a negative ad? >> does it mention hillary clinton? >> nope. >> does it have any image of hillary clinton? >> nope. aren't you suggesting she's bought by wall street? >> i'm not suggesting anything at all. >> reporter: tonight clinton returned to iowa, and sanders, who at 74 would be the holdest person ever elected president if he wins, released his medical report, asserting he's in very good health. >> you know what i'm thinking of doing? >> not with me. not with me. >> it was a tough decision. do i get involved in senior boxing, go for the light heavy weight for president? for president. >> reporter: now, hillary clinton is back in iowa tonight. she only just took the stage tonight, though. and because this contest is so tough, she does repeatedly have to go back to big donors, unlike sanders, who has more than 2.5 million online contributors. let's bring in our political director, the moderator of "meet the press," chuck todd. how is this playing there in iowa? any signs of a blow-back on the ground there? >> not from anybody that's thinking about supporting trump, and that's probably good news for him. look, he has figured out a way to steal the spotlight from this debate before it started, and there's already a lot of rumors circulating around here that he may figure out how to steal the spotlight after the debate is over, that maybe he shows up in the spin room or he figures out a way. and that's been, you know, his campaign in a nutshell is he figures out how to almost pull the rug out from under his opponent. as for the debate tonight, i think it's actually fascinating that trump's not on stage and instead the focus will be on ted cruz and marco rubio. you know, the other big news in our new nbc news/"wall street rubio has ticked up. rubio is now in a strong third-place position. what does that mean? ted cruz is hammering rubio with a new attack ad. tonight, lester, rubio v. cruz, this actually could be the showdown worth watching and the one that could extend if trump falters. >> a lot of things in play. chuck, thanks. a program note. last night we talked to bernie sanders. tomorrow night we'll have my conversation with hillary clinton on the trail in iowa. a final sprint before the voting begins. a warning now from the world health organization that the zika virus is, quote, spreading explosively. in this year alone, three to four million in north and south america could be infected with the virus linked to birth defects. the cdc says the number of people returning to the u.s. with zika is growing. nbc's tom costello has more. >> reporter: dr. whitney prince is one of a few americans who has experienced the zika virus as a patient. it was on her honeymoon in bora bora that she contracted zika through a once home, she developed a skrin rash, conjunctivitis, and a headache. >> feeling very worn out, tired, kind of dragging, and i actually ended up staying out of work for about a day and a half, mainly because of the joint pain, because it was painful to walk at that point. >> reporter: dr. prince recovered and she was not pregnant. no unborn child at risk of developing microcephaly. but in brazil today. nbc news was with this woman when she visited her doctor. her 2-year-old is one of thousands of baby who's have been born with microcephaly this year. while mosquitos carrying zika have not yet arrived in the u.s., 31 cases have turned up in 11 states and d.c. all of them involved travelers who contracted zika while abroad. in addition, 19 cases in port rico in one in the virgin islands. while experts some zika mosquitos will arrive in southern gulf states, they don't expect a massive >> there is always the slight possibility that we might see a major outbreak. we don't think that's going to occur, but we're going to be prepared for it. >> reporter: the reasons for the optimism, there's far less trash and stagnant water in u.s. urban areas. cities and towns spray for mosquitos here. cold weather acts as a barrier, and americans use air-conditioning and window screens to keep mosquitos out meanwhile, gina park is 18 weeks pregnant. she and her husband have now canceled an upcoming trip to mexico. >> we just thought it wasn't worth the risk to go. we just probably couldn't live with ourselves if something ever did happen. >> reporter: meanwhile, the national institutes of health today said it hopes to start clinical drug trials this year, but a zika vaccine could be years away. tom costello, nbc news, washington. let's turn now to a mystery that played out for hours late this afternoon in the new york area as reports started to stream in of what felt like an earthquake from the jersey shore all the way to long island and a failure rid of 911 calls. turns out it was actually a series of sonic booms caused by a military f 35 fighter jet based in maryland conducting flight tests up the new jersey coast. mystery solved. just a lot of frayed nerves left behind. >> we have breaking news on this tense stale mate in oregon at the federal refuge seized by government protesters. just four hold outs remain and we're now hearing things may be coming to a conclusion there. leader ammon bundy had urged them to stand down. bundy was arrested tuesday when violence erupted during a traffic stop and left one member of his group dead. now to an nbc news exclusive. we've gotten extraordinary access into iran and in a rare interview, the american educated head of iran's nuclear program reveals to nbc's richard engel interview before heard details about the controversial deal that lifted international sanctions on iran. >> reporter: little is known about how iran ended up making a deal the united states. but now in the first american interview since the deal, the head of iran's atomic energy organization told nbc news his country's supreme entrusted him with hammering out the details of the nuclear agreement, within limits. trust the americans. but okay. i trust you. you give it a try and see what you can do. >> reporter: ali akbar salah hi, an mit educated science. revealed for the first time conditions the supreme leader set. >> one condition is you just discuss the nuclear issue, no political negotiations. >> the ayatollah also insisted talks had to be quick and preserve iran's right to enriched uranium. >> the fourth condition was a condition that let's keep it for ourselves. >> reporter: you don't want to say what it is even now? >> not now. >> reporter: but he did want to talk about the u.s. to a level not seen since american diplomats were taken hostage at the u.s. embassy here 36 years ago. >> relationships, industrial cooperation, cultural cooperation. >> american factories opening here? >> well, we welcome them, yes, if they want. why not? >> reporter: but trust is hard to build. >> this photograph on- >> reporter: salhi keeps photographs of a a driver assassinated in an effort to slow iran's nuclear program. "e" claims israel did the claims with washington's tacit approval, allegations washington denies and israel won't confirm. there's a space here. do you think there will be a sixth? i know obviously you don't want that. >> i hope it's me. >> you hope it's you? >> yeah, because this is a source of pride. i told you. yeah. >> reporter: a wide gap still exists between the u.s. and iran and the zeal of its revolution remains just below the surface. richard engel, nbc news, tehran. there is more to tell you about here tonight. did you get shut out for adele tickets or maybe you paid double to see the boss? investigators say you're playing a fixed game. how they plan to crack down on it. also barbie is getting a new look. several of them, in we're back now with a major new investigation blowing the lid off the reason so many people get shut out when trying to buy tickets for a hot concert or sporting event. chances are it's happened to you, and it's not just because so many people are clamoring to go. investigators say it's a fixed game and as nbc's jacob rascon reports now, they're fighting back. >> reporter: everything about adele is speak,ctacular, fans will tell you, ebs september how impossible it can be to score a ticket to see her. it's a worldwide problem for so many of the hottest events. why is it often so difficult to get tickets at face value? now a three-year investigation by the new york state attorney general reveals nightmare scenarios for many concerts tickets are never available to begin with. >> artists, promoters, venue protesters will hold back tickets. they never make it to >> some shows had 70% of tickets earmarked for presale events. the report also found one trikt broker using a technique called a bot can pleedry scoop up tickets for resale. in one example, someone bought more than a thousand tickets in one minute for u 2's performance. >> it has many fans steaming. >> so frustrating. like really heartbreaking when you know you're doing it purposely so you'll pay three, four times the price. >> it's a niegs wade problem. it's everywhere. i can't think of a state in the country where this isn't a problem. and it happens at every major concert venue. >> reporter: your best shot at landing those must have tickets, experts say register for fan clubs to get early access or look for single seats. even then, there's no guarantee, leaving so many fans on a sour note. jacob rascon, nbc news, new york. when we come back, years ago today? questions so many are asking tonight as we tragedy. it was exactly 30 years ago when seven crew members boarded the space shuttle challenger and set off on an adventure. seconds later in a moment seared into the many of americans who watched it live and the many more who saw it replayed, the mission ended in a tragic disaster in the sky. nbc's tefn tibbles takes us back to the moment that forever changed american someplace exploration. >> and liftoff. >> on a clear but unusually cold cape canaveral morning, space shuttle challenger left this earth and headed for space. filled with anticipation and hope. but at 11:39 eastern >> challenger, go with throttle up. >> we have just seen the launch of the space shuttle challenger. there has been a major problem. >> reporter: the shuttle tragically disintegrated high over the atlantic, its crew of seven gone. including christa mcauliffe, the first teacher in space. her parents watched at the cape. her students were watching in new hampshire. some of those students and others across the country would later choose to honor her memory by becoming teachers themselves. today at ceremonies from arlington national cemetery to cape canaveral, wreaths were laid in remembrance. we are still reaching for the stars, from the mars rover on the red planet to stunning new pictures of pluto, from the probe new horizons. and of course the international space station where today a moment of silence was held. but it was on that decades ago that president ronald reagan postponed his state of the union address to deliver his poignant remembrance. >> the future doesn't belong to the faint hearted. it belongs to the brave. the challenger crew was pulling us into the future, and we'll continue to follow them. >> reporter: kevin tibbles, nbc news, chicago. there is a big change coming for new moms in the military. the pentagon announced that it will now grant 12 weeks of maternity leave to women across all branchs. that's good news for the army and air force because it doubles their leave time. bad news for the navy and marines because it cuts their leave back from 18 weeks. when we come back here tonight, barbie is breaking with the past. why the iconic doll historic makeover. finally tonight, a historic change for one of the most popular toys of all time. for generations, barbie dolls have presented an image of perfect beauty, and for many that's exactly the problem. but now as nbc's erica hill tells us, barbie is getting a whole new look. barbie, you're barbie debuted in 1959, she's tried just about every job. >> try it again. >> reporter: but one thing that never changed, her figure. until today. when toy maker mattel introduced three new barbie body types to better represent the shapes and sizes of real women. petite, tall, and curvy. >> i think it's about time that they changed shape. >> reporter: critics have long complained barbie's body was an impossible ideal, and there was growing pressure for more physically realistic dolls. mattel went back to the drawing board, building on additions made in 2015, which introduced more diverse options. >> society felt that a brand like barbie needs to be more in touch with the times and needs to be a better reflekds of the world girls are living in today. >> reporter: while barbie remained a best settler for matt lerks, 93% of girls have owned one of the 20% from 2012 to 2014, a slide that continued into 2015. >> more and more brands are recognizing that women and girls as consumers and as audiences, they need more. they demand more. they want more, and they'll spend more. >> reporter: mattel is hope ng the new dolls, available online now, in stores this march, will help to boost sales. >> times are changing. life has changed. we're all different shapes, different colors, different ethnicities. >> reporter: it just may be barbie's freshest look ever. erica hill, nbc news, new york. and that will do it for us on this thursday night. i'm lester holt. for all of us at nbc news, thank you for night. in -- the final gop debate before the caucuses is moments away. a lawmaker's overturned drunk driving conviction is raising questions. news 4 nightly starts now. you're watching news 4 nightly on your side in high definition. good evening, everyone. thanks for joining us tonight. i'm shelby sheehan. joe hart has the evening off. michelle fiori is in the spotlight tonight. she's weigh nothing on the why fiori plans to get even