Who did . Nightly news begins right now. From the Democratic National convention, this is nbc nightly news with lester holt, reporting tonight from philadelphia. Good evening. Coming off that soaring and passionate endorsement speech by president obama, tonight it is Hillary Clintons turn to tell her own story to this convention and to america. A speech she hopes will put not just a period on this week but an exclamation mark as she heads into the thick of the campaign. Like donald trump clinton arrived at her own convention with high negative approval numbers. It will be the proverbial elephant in the room when she takes the stage this evening. How will she address it . Nbcs Andrea Mitchell has details. Reporter the torch is passed. Tonight its her turn. After that embrace and the most ringing endorsement any president has given a possible successor in modern history. There has never been a man or a woman, not me, not bill, nobody more qualified than Hillary Clinton to serve as president of the United States of america. Reporter now its on her. New images of clinton with the president backstage. Then watching him deliver his speech. Shes been preparing hers for weeks. But afterwards went immediately into rewrite. Her top challenges tonight make the case she can be trusted. In our latest poll, donald trump beating her on honesty by 21. Shell acknowledge the problem tonight, as she did recently. A lot of people tell pollsters they dont trust me. Reporter she knows she has to work on that . She will acknowledge theres a lot of voters out there that are probably not all that enthralled by donald trump but may remain skeptical of her. Reporter her second challenge make a sharp contrast with trumps message, what the Campaign Says is his focus on himself. I alone can fix it. As i recall we had a revolution to make sure we didnt have someone who said i can fix it alone. Reporter but perhaps clintons biggest challenge, not being overshadowed by the powerhouse lineup that has already gone. Her husband, with his personal storytelling. In the spring of 1971, i met a girl. Reporter Michelle Obama. What i admire most hillary is that she never buckles under pressure. Reporter and president obama. You cant afford to stay home just because she might not align with you on every issue. Youve got to get in the arena with her because democracy isnt a spectator sport. America isnt about, yes, he will. Its about yes, we can. Reporter right now the campaign knows these rates could go either way. Tonight a critical moment to have the stage to herself and millions watching. What Hillary Clinton needs to do marry a biography with what she wants to do as president. It sounds easy, but its never come easy to her. Reporter and one more challenge for clinton when voters say they want change, how can she persuade them she isnt the status quo . Lester. Andrea mitchell on the convention floor, thank you. Hillary clintons speech tonight will be tough to top the stemwinder delivered on her behalf by president obama. She needs him to help her win in november and he needs her to help cement his legacy. All that converging in a rousing rebuke of donald trump and an appeal to republicans from the stage behind me. Heres peter alexander. Barack obama. Reporter it was one of the biggest speeches of his life, and this one wasnt about him. Tonight i ask you to do for Hillary Clinton what you do for me. I ask you to carry her the same way you carried me. Reporter a speech to preserve president obamas legacy in the hands of a trusted heir, but in this Chaotic Campaign year there were other goals, too. With donald trump subpoena a controversial candidate, the president wasnt just targeting democrats. Tonight our exclusive interview with his speech writer cody keenan. Was this speech in part intended to reach out to disaffected voters and moderate republicans . It was an attempt to reach out to everybody, really. Reporter still recent polls show many republicans remain up for grabs. 60 of them dissatisfied with their nominee, which is why the president made this unmistakable name drop, a signature phrase from a republican icon. Ronald reagan called america a shining city on a hill. Reporter and it wasnt just the president. Clintons running mate tim kaine appealing to republicans. If any of you are looking for that party of lincoln, weve got a home for you right here in the democratic party. Reporter democrats also inviting former new york city mayor and former republican michael bloomberg. Trump says he wants to run the nation like hes running his business . God help us. Reporter keenan trading six drafts with the president who stayed up till 2 30 thursday morning revising his remarks after watching his wife. Because this right now is the greatest country on earth. Like any potential marriage. They make each other better. Reporter did it work . Republican voters today responding. His description of the last eight years didnt fit reality, but he sure got you into the magic of his words. It was pandering to try to make me fear to vote for hillary out of fear of donald trump. Thank you. Reporter after a historic night the president confident the case for clinton was made. When it was done, what did he say . He said, i think that worked. Reporter thats it . Thats it. You know. Reporter peter alexander, nbc news, philadelphia. Also part of the fullcourt press tonight is former and perhaps future first daughter, Chelsea Clinton, who has grown up, quite literally, before our eyes. Now a mother herself, hoping to reveal a side of her mother that the country might not know. Nbcs Kristen Welker has her story. Reporter the world has watched her grow up from a preteen at the white house to becoming a mother of her own. And tonight Chelsea Clinton will step into an even brighter spotlight, introducing the most important woman in her life her mom. Telling matt lauer. Im going to try really hard to not cry. I think my heart will burst. This election is so important to me because im now a mom. Reporter clinton has been a strong presence on the trail. But during tonights speech, chelsea will leave the policy behind and get personal. I just hope that people understand even a little more when im done than when i started about why i love her so much and admire her so much. Reporter the 36yearold who now helps run the Clinton Family foundation was born into the world of politics. As a child, the public only caught a few glimpses of her like during the 1992 Democratic National convention. But in 1998 with her parents mired in the lewinsky scandal, chelsea became a Political Force of her own, walking hand in hand and humanizing one of their toughest moments. Proud to be my mothers daughter. Reporter chelseas challenge tonight softening the image of her mother, who is struggling with historically low favorability ratings. Chelseas going to beam with pride about the accomplishments of her mother and the historic nature of tonights speech. Reporter and the bar is high. Her friend ivanka trump drew rave reviews after introducing her dad last week. You will never again have to worry about being let down. Reporter the bitter battle between their parents has clearly taken a toll. I dont expect her to always have to defend her father. My mothers not engaging in divisive rhetoric. Reporter chelsea now becomes first person ever to have both parents nominated for president , already making her own mark on history. Kristen welker, nbc news, philadelphia. We do hope youll join us tonight along with chuck todd, savannah guthrie, tom brokaw and our entire team. Our primetime coverage starts at 10 00 eastern, 7 00 pacific here on nbc. Donald trump trying to calm the youp roar over his wish for russia to hack his rival Hillary Clinton. Trump now saying he was merely being sarcastic. Questions are being raised about melania trumps past on the heels of her plagiarism scandal. We get all that from hallie jackson. Reporter tonight two kinds of defense for donald trump. First on his invitation to russia to hack Hillary Clinton. Russia, if youre listening, i hope youre able to find the 30,000 emails that are missing. Reporter now, with new fallout, a new explanati explanation. When im being sarcastic with something of course im being sarcastic. Reporter but for president s, even a joke can have real consequences as Ronald Reagan learned in 1984. Ive signed legislation that will outlaw russia forever. We begin bombing in five minutes. Reporter he wasnt serious, but the soviet union was. Resulted in a soviet red alert. There just isnt much room for error. Thats why matters of International Relation have to be conducted with due seriousness. Reporter trump also facing fire about something else. Charges his wife didnt actually get the architecture degree she claimed in her online biography. Those questions surfacing after her Convention Speech in which she used some of the same lines Michelle Obama did in 2008 and the College Graduation claim appearing in the official rnc program. Her bio and the rest of the website now redirecting to her husbands. Mrs. Trump tweeting her site didnt accurately reflect her current business. I grew up in slovenia. I went to school there. I started design and architecture. Reporter the Trump Campaign declining to comment on the college claims or release documentation backing them up even after trump himself back in 2012 offered a reward for anyone who could provide president obamas documents, his College Transcripts and his birth certificate. Donald trump tonight speaking here in iowa hinting at attacks to come across the aisle. Telling the people here that he wanted to hit the speakers a tt Democratic National convention so hard for what he described as the lies theyre telling about him. Hallie jackson, thank you. Lets turn to the new alert over the zika virus. Health officials are investigating more cases of the investigation suspected of being transmitted by mosquitoes for the first time in the United States. The continental u. S. A potential game changer in the fight against zika here and its resulted in the fda halting Blood Donations in parts of florida. Nbcs Kerry Sanders has much more on this for us. Reporter scientists fears about zika in the United States appear to be coming true. Today federal Officials Say four new cases turned up in cases in south florida and theres growing evidence they were transmitted by mosquitoes in this country. We were fairly certain that this would ultimately happen because we have so many travelrelated cases in the United States. Reporter the fda told Blood Donation centers in miamidade and broward counties to cease collecting blood immediately until theyre able to test each individual unit of blood collected. In south florida most of the donations are collected by an Organization Called one blood that says as early as tomorrow they will begin testing all of their Blood Donations for the zika virus. So far more than 1600 people diagnosed with zika in the continental u. S. Including more than 400 pregnant women, but those cases were contracted by people traveling into the u. S. From other countries or puerto rico. Aggressive Mosquito Control efforts now under way as pregnant women and their doctors are on edge. If in fact the cases do turn out to be confirmed thab been acquired from the mosquitoes, this is no longer a warning. Reporter its an urgent call for people to be on the lookout for any zika symptoms and take action to protect themselves against mosquitoes. Kerry sanders, nbc news, miami. A startling sight when sparks dpan shooting out of an engine a passenger captured on a cell phone video. The flight was forced to turn around and land safely. The airline says the engine was not on fire, explaining those sparks are indications of what they call a compressor stall, a disruption of air flow in the engine. An emotional day in baton rouge, louisiana, as Vice President joe biden joined hundreds of others to honor three Law Enforcement officers killed by a gunman in a shocking ambush over a week ago. Attorney general Loretta Lynch was also on hand at the mel moral for officers matthew, gerald and Montrell Jackson and sheriffs deputy brad garafola. The murder mystery that gripped the nation. Why the man convicted of killing washington, d. C. , intern chandra levy is now going free. Also caught on camera, what is that mysterious light in camera, what is that mysterious light in 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. And the otezla prescribing information has no requirement for routine lab monitoring. Dont take otezla if you are allergic to any of its ingredients. Otezla may increase the risk of depression. 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You can make it grrreat kelloggs frosted flakes gives you the sweet spark to go all in and let your great out. Theyre grrreat a stunning twist has thrust ab infamous murder mystery back into the national spotlight. It was the summer of 2001 in the months before 9 11 when the country was consumed with the disappearance of government intern chandra levy. Now all these years later prosecutors are dropping charges against the man once convicted in her death. Our justice correspondent Pete Williams has late details. Reporter with no one convicted, chandra leavys murder remains a mystery, killed while jogging in 2001 at age 24 in washington on an internship. At first police focused on a congressman, gary condit, who had an affair with her, but he was ruled out. Seven years ago prosecutors charged ingmar guandique, and served a prison sentence for attacking two other women in the same park where her body was found. Guandique was convicted in 2010 but was given a new trial when his lawyers said a key witness lied in court. Now with his retrial scheduled to start in october, prosecutors are dropping the case. In a statement they cite unforeseen developments that were investigating over the past week. Levys parents were notified this morning. They have fought to keep the case open. I only wish that we can get the right person in whoever did what happened to my daughter. Reporter legal experts say the case has suffered from depending on jailhouse informants. There was no forensic evidence, there was no dna, no fingerprints, no witnesses, no Security Camera video footage, anything of that nature. Reporter guandique will be turned over to immigration authorities who will seek to deport him, but Chandra Levys murder remains unsolved. Pete williams, nbc news, washington. Were back in a moment with some beloved neighbors moving away after decades on this famed my business was built with passion. 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