this is "nightline." tonight, this is what the international refugee crisis looks like from the ground. as streams of migrants flee war-torn countries, a new fight begins finding somewhere else to go. >> it's an incredible scene. >> "nightline's" own is there. and i made a mistake. hillary clinton opens up about her e-mail scandal. >> i'm sorry about that. i take responsibility. >> from donald trump and joe biden, no one's off limits. and victorious. a sibling showdown at the u.s. open, as serena williams beats

venus williams. from the early years to decades of world fame. one winner tonight, but sisters and champions forever. but first, the "nightline" five. if you're suffering from constipation or irregularity, take dulcolax. unlike miralax dulcolax offers relief. this gel rushes three pain fighters deep into my muscles. it's fast acting, penetrating relief. >> salonpas, when and where you need it.

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tonight, an intimate look at the international refugee crisis, as men, women, and children cross over european borders by the hundreds of thousands of some of those countries are warning this evening they can't keep up. my "nightline" co-anchor, dan harris is on the ground. dan? >> reporter: good evening to you from the port on the beautiful greek island of lesbos. norm think would be filled with high-end tourists, but tonight it is packed with refugees. thousands of them have gotten stranded here. this is a situation that has created anger, even violence. over the past 36 hours we have witnessed some extraordinary events unfolding here. we were right there today as refugees finished a perilous leg on their journey to freedom, packing these rickety illegal smuggling boats from turkey and

sayiarriving here on the greek island. these families have risked everything, their lives, their family, everything they know and love to arrive here in greece. the relief painted all over the faces of the parents. what's her name? >> fatimah. >> reporter: welcome to greece, fatima. these people have just taken a massive risk. massive risk. people have died crossing this strait. i'm very glad you made it safely. >> thank you, sir. thank you very much. >> reporter: those who make it are met by volunteers like hannah louisa who traveled from denmark to hand out supplies and give basic medical attention. why did you come here? >> i just came because i needed to do something. >> reporter: how would you describe this situation here? >> totally chaotic. >> reporter: chaotic, yes, but in these first few moments often

jubilant. that initial elation evaporates for these new arrivals when they realize they have a 30-mile walk in front of them in the searing heat. and then this. after making the hike, the refugees have been running into a bureaucratic blockade. the government here on this island of roughly 85,000 people has been unable to speedily process everyone, to give them their papers and send them along. these refugees, fleeing war and terror in places like syria and iraq want to move on to mane land greece and up through germany where they've seen those pictures of immigrants being warmly welcomed. but instead, they've been marooned here, running out of money and patience. there have been violent clashes with police. the situation here on lesbos has created some bizarre contrasts. this idyllic island, a place where aristotle once lived now

teeming with refugees. this quaint little city center would normally be filled with strolling summer tourists, but it is now, as you can see, overrun by literally thousands and thousands of refugees living in tents with all their worldly possessions, their children and their hope for the future. and the local government here is completely unprepared to deal with it. in a squalid camp hastily set up on a disused go-cart track, we met many angry jeff grefugees including this mother who said she was trying to get her son to germany for medical treatment. it is just stunning. we are on a paradise island in europe. >> yeah. >> reporter: and we are in a refugee camp. >> yeah, i've been doing it for 20 years, and i never thought i would be doing emergency response in greece. >> reporter: curt day says that

the rules for leaving seem to change constantly. >> they are upset with any delays associated with being able to get off the island. >> reporter: sure enough, as we're rolling, kirk gets a phone call. >> three boats arriving, and we'll be running to get all the refugees we can off the island, that's a capacity of 6,000 people. >> reporter: hours later, we're on a soccer field that's been transformed into a field of dreams. officials have set up an emergency processing center, which they say will run 24 hours a day until they can deacon jest this island, and it appears to be working. >> i'm very touched. extremely touched. >> reporter: alexandra works for the united nations. >> to have people walk by and say thank you, that must be an incredible moment. >> i'm touched. >> reporter: they are celebrating. >> yes, thank god. >> reporter: what is it like for you? >> don't make me cry.

>> reporter: and look at the tears that come when that mom we met earlier finally gets her papers to leave. >> thank you, thank you! >> reporter: there really are no happy endings on lesbos, though, as the newly processed refugees clamor to join the first boat out, it is deadly. this is a combustible mix of hope and chaos. so many people lined up clamorring to get on this boat, and a few officials trying to maintain some sem blachblance o order. it is entirely possible someone could get crushed. these people are still facing a long and arduous journey ahead. that first boat load arrived on the greek mainland and headed north. but they are heading toward a

potential buzz saw in hungary. the world has truly been horrified by the images of europe's refugee crisis, families running through cornfields, scrambling under barbed wire and penned into camps. then there are the people turning a profit on all this, like the smuggler in this video obtained by the bbc, discussing the sale of those dangerous little boats that refugees use to cross from turkey into greece. [ speaking in foreign language ] >> reporter: critics say this refugee crisis is a slow-motion disaster that the global community, including the people in the white house, should have seen coming. after all the war in syria, which has displaced an estimated

11 million people, has been grinding on without resolution for years. tonight, while germany is actively resettling tens of thousands of immigrants, the uk and france are promising to step up as well, and the obama administration now says it will boost its response, potentially accepting thousands of these refugees into america. >> everybody moved by a sense of urgency here. >> reporter: something has to be done and soon. because, as we saw on the beach in lesbos today, the desperate people, they just keep on coming. tonight here at the port, it is still crowded but much less chaotic. in the past day or so, they've managed to send thousands of refugees off the island. while that will ease the situation here, what it does is essentially move the problem up north. this crisis is far from over. byron, back to you. >> dan, thank you for that report. next, democratic

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presidential candidate hillary clinton has survived her share of scandals, but facing an upcoming date with congress to testify about her private e-mail server some are wondering if this might be her undoing. tonight, clinton gets candid in an exclusive interview with david muir. >> secretary clinton, thank you. >> thank you, david. >> when voters were asked, what is the first word that comes to mind when you think of hillary clinton, words like liar and untrustworthy were at the top of the list. does this tell you that your original explanation about the private server, that you did it could carry one phone out of convenience, that this didn't sit well with the american

people? >> well, i don't like hearing that. i am confident by the end of this campaign people will know that they can trust me and that i will be on their side and will fight for them and their families, but i do think i could have and should have done a better job answering questions earlier, as i look back at it now, even though it was allowed. i should have used two accounts of the one for personal, one for work-related e-mails. that was a mistake. i'm sorry about that. i take responsibility. and i'm trying to be as transparent as i possibly k i am looking forward, finally, to testifying before congress. something i've been asking for for nearly a year. >> and, so, as you sit here, millions watching tonight. >> mm-hm. >> did you make a mistake? >> i did. i did. as i said, it was allowed. and there was no hiding it. it was totally above board. everybody in the government i communicated with, and that was a lot of people, knew i was using a personal e-mail. but i'm sorry that it has, you

know, raised all of these questions. i do take responsibility for having made what is clearly not the best decision. >> the intelligence community's gin spektser general telling abc that after reviewing those e-mails that two of them carry the classification of top-secret. that both e-mails were classified when they were created and remained classified now. one was about drones. one was about north korea's nuclear program. i'm curious, does this mean classified information passed through your private server? >> well, there is still, as you know, a dispute. the state department disputes that. i understand why different agencies have different views, and i respect that. it does not change the fact that i did not send or receive any information that was marked classified at the time. >> at the time marked classified. >> mm-hm. >> but let me ask you, for the rest of us, the average voter and average viewer out there who might wonder, how can some of these e-mails be classified and labeled as top-secret today.

>> mm-hm. >> what changed in them so significantly that you wouldn't have seen red flags even just a couple years ago as secretary of state, that you of all people would have known. >> yeah, that's a very fair question. and i think there are a couple of answers. one, sometimes events do proceed in a way that maybe there's a case being brought against somebody, maybe even a terrorist. and all of a sudden everything is classified. >> but north korea's nuclear program, wouldn't that be classified? >> there's a lot of public information about their nuclear program. i don't know the specifics about the one that they are claiming is classified. >> she makes it clear this is not a criminal investigation. we then ask her about the other news of the day, joe biden. voters chanting this weekend, run, joe, run. >> you were once ons the same team inside the white house. you would often have breakfast with the vice president. would he make a good president? >> well, i like joe biden a lot. and i think he is a great vice president. if he gets into this election,

there'll be lots of time to talk about, you know, what he wants to do. >> would he make a good president? >> well, you know, i think he could be a good president. there's no doubt about that. >> she says he deserves to test the waters, and then another candidate. donald trump. i want to read you something jeb bush's son recently tweeted. can't wait for this summer reality tv show to be over. >> that's cute. >> but is it a reality show? or are we witnessing something real here? >> well, that's going to be up to the republicans and the republican primaries to determine. you know, i'm always a little amused when people get into politics and they think that all you have to do is give speeches and the more colorful you are, the more dramatic, the more vehement you are, that's leadership. >> do you think donald trump is just a leader of rhetoric and speeches? >> well, he won't tell you how he would do anything. >> i want to know in your most private of moments, is there ever an instance when you ask

yourself, why am i doing this again? >> yes. of course. because it really is hard. and it's, it's something that, you know, just demands everything. physically, emotionally, spiritually. it is just 24/7. i cherish and love this country. it gave me, you know, opportunities far beyond anything my mother, my father could have had. >> is your mother's voice in your ear? and if so, give me one line that you repeat to yourself. >> as you probably know, my mother had a terrible childhood. she was abandoned by her parents, rejected by her grand parents. she was literally working as a housemaid at the age of 14. and she told me every day, you've got to get up and fight for what you believe in, no matter how hard it is. and i think about her a lot. i miss her a lot. i wish she were here with me. and i remember that. and i don't want to just fight for me. i can have a perfectly fine life

not being president. i'm going to fight for all the people like my mother who need something in their corner, and they need a leader who cares about them again. so, that's what i'm going to try to do. >> i'm david muir for "nightline" in new york. and next, from oprah winfrey to donald trump, the stars came out to see serena williams. the latest choice for frequent heartburn. get complete protection. nexium level protection. thiproof of less joint pain. and clearer skin. this is my body of proof that i can fight psoriatic arthritis from the inside out ...with humira. humira works by targeting and helping to block a specific source of inflammation that contributes to both joint and skin symptoms. it's proven to help relieve pain,

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and finally tonight, serena williams, emerging victorious just hours ago defeating big

sister venus to win a grand slam, capping off a journey from compton, california to the u.s. open. two of the world's greatest athletes, competitors tonight who have never let sibling rivalry tarnish their bond. a packed house, hard-fought slugfest and a final serve to victory. serena williams beating out sister venus in the u.s. open quarter finals. >> it's going against your best friend and at the same time, going against the greatest competitor for me in women's tennis, so it was really difficult today. >> the number one ranked serena inching closer to the calendar grand slam title. 14 years ago today, sisters, 14 million viewers looking on. back then, venus was the favorite. but this year a different story.

33-year-old serena williams is now the number one ranked player in the world. serena speaking to espn about the unique challenge of playing her sister. >> venus has done everything for me. i remember there were times when if i didn't have money, lunch money for school, she would skip lunch and give me her money. so it was, like, how could i take something from someone else who has protected me her whole life. has done everything for me her whole life and who would starve for me. >> these super siblings growing up in compton, california, first faced off in 1998. in australia. venus, then 17 years old, serena, 16. their careers forever linked. tennis fans around the world embraced them both. serena has won 21 titles, venus, seven. with tonight's win, serena is

one step closer to becoming the first player since 1988 to clench the calendar grand slam title, taking all four major tournaments in one year. rivals, champions, always sisters. it's been said, a sister shares childhood memories and grown-up dreams. tonight we've retreated to both. and don't miss the u.s. open coverage tomorrow on espn. thank you for watching abc news. tune in to good morning america tomorrow and as always, we're online