in the "nightline." >> tonight the desperate march north along the migrant trail. central americans fleeing their homelands by the tens of thousands to escape brutal gang violence. the road ahead is dangerous. many facing death for the hope of a new life. hillary clinton hits the campaign trail with president obama. >> fired up! >> the investigation into her e-mails may have ended with no charges but will it cost her votes? >> it's a disgrace! and they're like another member of the family, but what would you do if your dog acted like this? anxiety, separation issues, and depression. more dogs are being diagnosed with very human ailments and more owners are putting their pets on pills. first here tonight the

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good evening. tonight see a side of america's bitter immigration debate you almost never get to see. we know about donald trump's plan to build a wall and president obama's stinging setback in the supreme court for his plan to offer legal status to millions of undocumented

immigrants. what is largely out of view is the human drama and sheer danger of the journey so many people are attempting to make even as i speak tonight. abc's matt gutman is in mexico on the migrant trail. >> this is the bridge over the river. >> reporter: the river that separates mexico and guatemala. >> this is the legal way to do it. if you have papers. >> reporter: at the bridge, the only official border crossing for miles. we're tracing the first and one of the most dangerous stretches of the migrant trail. traveled mostly by central americans trying to escape the brutal gang violence back home. a few blocks from the bridge we meet edwin and jose. they come from el salvador, the murder capital of the world. they're beginning their second attempt to reach the u.s. the uncertain road ahead is more appealing than the horrors they're leaving behind.

he says the situation in el salvador is very bad. violence, poverty. there's nothing there. like most central americans fleeing their homeland, they will cross into mexico illegally. no passports among the treasured belongings in those tiny backpacks. jose wears his reason for flight on his back and his arms. he shows us the nickel-sized scars from a shotgun blast. he says, thank god the gangs didn't kill me, because they tried. that's why we're the victims in this situation. we don't have any other options. if i go home, i could die." crossing the river, edwin and jose both know that once in mexico, their journey will become much more treacherous. when migrants are smuggled across this river to mexico, they're entering what human rights advocates call a death trap for them. mexican authorities are sweeping up migrants in record numbers before they even reach the u.s.

most are deported. but mexico enforcing its own immigration laws more than ever has created another crisis. with bandits and human traffickers preying on migrants still looking for ways to get north. edwin and jose disappear over the riverbank. and we rush through the legal crossing on that bridge to try and catch up with them. traveling north through immigration checkpoint after checkpoint. eventually reaching a nearby shelter, a church-run safe haven for road-weary migrants. >> there we have a little chapel. >> reporter: father florigoni is a priest with a prophet's beard and says we're in the midst of a humanitarian crisis of biblical proportions. >> children, women, and other people. >> everybody is trying to get out. >> they come here. sometimes with bullets still in their bodies.

asking just for a chance. >> reporter: that's why he describes most as refugees rather than migrants. like carlos horkwho fled el salr with his wife and three small children. carlos tells us families in el salvador are affected the most. his goal as a father is to keep his family safe. the shelter is crowded but father flor tells us less so than in years past. and no sign of edwin and jose. so wedrive towards riaga the southernmost stop for the freight trains that migrants calla bestia, the beast train. it's not an affectionate term, it's a term coined because so many people get hurt, maimed, killed along this train. it's one of the ways so many of these migrants get extorted. imagine climbing on this then while it's moving. but it is still the most efficient way to get north.

we spot this trio walking a trail by the railroad tracks. his name is luis and he's just 19 years old. also from el salvador. he hasn't seen edwin or jose but has followed the same route almost 200 miles by foot. he leads us to a nearby shelter. you all speak a little english? >> reporter: the winds of violence from further south also sweeping in this group of destitute teens. >> this is all we have but more cookies if you want. >> reporter: some extra cookies in our car helping to stave off their hunger. >> are you afraid? >> reporter: and before they're allowed inside, they're frisked and searched. the shelter owners say it's a necessary indignity to keep the shelters safe. >> they're all willing to withstand this, to undergo this, because they know this is the first time they can actually have a bed to sleep on and probably the last time for a very long while. >> reporter: it's just a temporary reprieve. migrants have only three days in

most shelters. but even here, beyond the reach of immigration authorities and most gangs, not everyone feels safe. even the people here you can't trust? >> you can trust nobody. i can trust me. but i can't trust that. >> even your own shadow you can't trust. >> reporter: he's 22, asked us not to show his face because even here he fears retribution from the ms 13 gang. >> they beat you up, bashed up your elbow, took all your money, took your brand-new phone? >> reporter: hansel's story is heartbreakingly common. according to the mexican government, three-quarters of those who pass through this area will be assaulted. we continue looking for edwin and jose. that's the pair we lost back at the border. after two days they finally responded to our texts. they tell us they're hiding near the train tracks and our driver thinks he knows where they might be.

>> haven't found anything. and our guys are nowhere in sight. >> reporter: after nearly an hour -- >> we just got a text from them that they were caught by immigration police and are in a van being taken somewhere. >> reporter: and in a sad glimpse into this unending cycle, a final text from jose. he and edwin are being deported. and jose tells us he and edwin will try the journey yet again. back at the shelter we check in with the group from honduras who after settling in share a moment of ease. hyena cackles and ribbing. acting like the boys that they are. it's a brave facade that shows cracks during the shelter's evening prayer. an uncertain future for them and their loved ones back home brings tears, too many for their hearts and their dirty sleeves to absorb. the boys the priests and sisters

bless can't hold them back. when you were crying just now, what were you thinking about? parents, family. it's hard. do you think you may never see them again? >> maybe, i don't know. >> reporter: we stayed in touch with them. four making it to the u.s. the others sent back. and in many ways they defy the odds. because after the prayers, i asked the priest how many he thought would make it. he says maybe 30%. probably less. for "nightline," i'm matt gutman, ariaga, mexico. next, if you're pet's got behavioral issues, should you put him or her on prozac? millions of american pets are on anti-depress ants. why some people are questioning this trend. first, your voice, your vote. it was a day of head-spinning development in the presidential

race. >> i'm fired up. hillary got me fired up. >> president obama and hillary clinton, one-time rivals, today side by side for the first time in this race. >> there has never been any man or woman more qualified for this office than hillary clinton. >> that ringing endorsement coming just hours after an fbi investigation slammed clinton for using a personal e-mail server during her time as secretary of state. a stinging rebuke. but no charges recommended. >> although we did not find clear evidence that secretary clinton or her colleagues intended to violate laws governing the handling of classified information, there is evidence that they were extremely careless in their handling of very sensitive, highly classified information. >> an almost audible sigh of relief from the clinton camp but her likely opponent's response swift and biting.

donald trump tweeting, the system is rigged. >> she went to extraordinary lengths to carry out an end run style purge of her e-mails. like a criminal with a guilty conscience, clinton had her lawyers delete, destroy, and wipe away forever 30,000 e-mails. >> trump tonight going so far as to imply that clinton bribed the attorney general. >> the attorney general is sitting there saying, if i get hillary off the hook i'm going to have four more years or eight more years. but if she loses i'm out of a job. it's a bribe. it's a disgrace. >> but earlier today, sleefves rolled up, the president throwing jabs of his own. >> everybody can tweet. but nobody actually knows what it takes to do the job until you've sat behind the desk. tak.

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we're taking another look at a new wrinkle in the debate over whether americans are overmedicating for what ails us psychologically. not only ourselves and our children but also our pets. here's abc's david wright. >> reporter: at the end of her work day, morgan hates to keep her partner waiting. >> racing out the door, running to get the subway. >> reporter: it's not so much that he's jealous, he just misses her more than he should. >> there is a part of me that feels guilty just because i know that when he gets stressed, he is very distraught. and it's hard to watch. >> reporter: unconditional love

isn't always healthy. >> hi! i know, i know -- i know, it's okay -- >> reporter: morgan accepts that about hatchi, a puppy who suffers from a very real, very human disorder, separation anxiety. >> hatchi digs at the floor. and he digs at the door. he bites the molding. and this is really all in an effort to get out of the apartment. >> reporter: and like an anxious human, there's powerful medicine that can help. that's right. this melancholy mutt is on doggy anti-depress ants, a sort of prozac for puppies. hatchi isn't alone. nearly 3 million dog in the u.s. are on anti-anxiety meds right now. let's not even get into cats. >> the problem is just like with us, we often turn to the drugs as the first line of treating the problem. i think that's the mistake. >> reporter: researcher and writer laurel brakeman, author of "animal madness," says our

pets have deeper emotional lives than most of us give them credit for. what sort of emotional complexity is there for a dog? we like to think that the dog is wagging its tail because he's happy to see you when you come home. when part of you suspects maybe it's because he's hungry. >> we're like that too, are we happy when we sit down in a restaurant because we're about to eat or because we're with good friends? it's safe to say other animals, particularly dogs, can be happy and sad and anxious and fearful. >> reporter: in a world of pampered pooches, where's the line between compassionate concern and full-blown crazy? >> it's so exciting, look! >> reporter: in "legally blonde," elle woods was a bit too present for her dog. >> you see a big blue ribbon -- >> reporter: how about "best in show"? >> go to the hotel and get busy bee! >> this is albert sign einstein. >> reporter: for ann marie it's not about pampering her pooch,

she's worried about albert's mental health. >> i take him for a walk, he's so nervous. he looks right to left, his tail is down. oh, yes, you can do it! he'll stop and freeze and be trembling very, very strongly. it makes you want to be able to give him a drink or something. >> reporter: after a series of failed behavioral treatments, albert was diagnosed with extreme anxiety. and the vet prescribed prozac. >> i knew that prozac really helped people. and i knew albert really needed help. >> reporter: but that diagnosis wasn't cheap. therapies and treatment costing upwards of $5,000. in fact, consumers nationwide are estimated to spent more than $7 billion on pet meds every year. more than ever before. >> and we're going to present him with our closed fist -- >> reporter: hatchi is meeting with trainer erika. >> he's like, that's what you were looking for, okay. >> reporter: prozac gives him that extra little help to succeed, according to his owners. >> you have to do the behavior

modification, you have to be extremely diligent and dedicated, because prozac's not going to solve the problem. >> he's just howling. >> reporter: morgan and jason show us hatchi in full-blown panic attack. he's been alone five hours. >> he's pacing. now he's whining. so he's clearly stressed. >> keeps going to the door. >> reporter: and this video, watch as hatchi opens the refrigerator door. >> that's not half as bad as what he can get. and that's very stressful. >> reporter: we take it to dr. brakeman. >> he's howling even as he has his head in the refrigerator, poor thing. >> heartbreaking, isn't it if. >> heartbreaking, it's so sad. he definitely has separation anxiety and perhaps he could benefit from medicine. >> reporter: preparation pad pet ownership isn't for everyone. >> this is a brain-altering medication. that's a really scary thing. do i want to alter my dog's brain? yes, when it causes him so much fear and anxiety that he has to

dig at a door and try to let himself out. >> reporter: at least for now the drugs are working for hatchi. >> it's tremendously helped. prior to putting him on this medication, he could not be alone for more than two hours. now the seven, eight-hour mark. >> reporter: albert, while skittish, is finally able to make it around central park. >> okay, all right! >> reporter: a spoonful of sugar and perhaps a dab of peanut butter helping the medicine go down, and helping the whole family relax. i'm david wright for "nightline" in new york. next, the american previously best known from reality tv now wowing at wimbledon. after beating the world's best player, can sam querrey go all the way? what about serena and venus? are we looking at a sibling rematch? i'm billy, and i quit smoking with chantix. i decided to take chantix to shut everybody else up

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finally here tonight, the fascinating questions looming over wimbledon. can the little-known american win the men's finals? will the williams sisters once again go head to head?

here's abc's nick watton night. >> o say can you see! sam querrey through to the last stage! >> reporter: smiling sam querrey, 6'6" san franciscan flaying a french man. he's dispatched novak djokovic, world number one all-time great. >> exciting match, it was something fun. i played really well, something i'll always remember. >> reporter: he was previously best known for bad dancing on vine. ♪ >> what's your celebrity crush? >> taylor swift. >> reporter: and bravo's celebrity matchmaker. if he wins he might have a date for the semis. >> i haven't felt many nerves. >> reporter: serena survived a slip slip slip and threats to sue an umpire. >> what i say on the court, whether smashing my rackets or in the heat of the moment, i have no plans, no future of suing wimbledon. >> venus williams back where she belongs at wimbledon! >> reporter: 36-year-old venus