tonight, breaking news as we come on the air. late today, joe biden and kamala harris for the first time appearing together as running mates, making their case. president trump already responding tonight. the former vice president and his running mate, senator kamala harris, appearing together in delaware, walking out in masks. socially distanced. joe biden saying he has no doubt he made the right pick, that her story is america's story. biden referencing trump's attacks already, calling harris nasty. saying is anyone surprised that donald trump has a problem with a strong woman? senator harris then saying she's ready to get to work. that whenever she's had doubts about these times, she thinks about the doctors and nurses on the front lines, the farmers, the factory workers. on racism and systemic injustice, she said there is a new coalition of conscience. and what she said about her friendship with joe biden's late son, beau. and what she said about father

and son. the former vice president with his head down. the emotion on his face. president trump speaking right after, addressing the pandemic, pointing to the markets, as he and his campaign deliver competing messages on this new biden/harris ticket. and president trump saying again today suburban housewives will be voting for me. and his reason why. also tonight, the new and dire warning from the head of the cdc. dr. robert redfield on masks tonight. saying that he's not asking some of america to do it, that we all have to do it. warning we could have the worst fall in u.s. history if we don't. the flash point tonight over opening schools. more than 1,000 students and staff quarantined in one district. and entire high school shut down. and the new model, what it warns when it comes to several major cities in the u.s. and tonight, the study here on different types of masks. which ones protect you best and the ones that might not help at all. overseas tonight, the horrific pictures coming in. the deadly train crash. several cars derailing. first responders searching the

debris. the images coming in. there's news tonight about the fate of college football this fall. the new announcement. and the late-day storms from washington, d.c. to philadelphia, right into new york city. good evening and it's great to have you with us here on this wednesday night. we have a lot to get to. and we begin tonight with the moment that played out late today. for the first time, joe biden and kamala harris appearing together as running mates. the former vice president and his history-making choice for vice president, senator harris, both wearing masks as they entered that high school gym in wilmington, delaware. biden introducing his running mate, the daughter of immigrants. and now the first black woman, the first asian-american on the presidential ticket of a major party. saying her story is america's story. harris then telling joe biden she is deeply honored, sharing her connection to the biden family. her friendship with biden's late son, beau. there was a moment when she shared a story about father and son. what beau once told her about

his dad. the emotion on joe biden's face. she then turned to president trump, his handling of the pandemic, the lives lost in this country, the jobs lost, saying america is crying out for leadership. the running mates were then joined by their spouses, standing on opposite sides of the podium. social distancing in this pandemic. just another sign of these extraordinary times. and senator harris and a nod to her career as a d.a., a state attorney general and her role in this upcoming campaign, she said the case against donald trump and mike pence is open and shut. of course, president trump sees this very differently. he's responding tonight, calling harris a disaster. abc's mary bruce leading us off from wilmington. ♪ >> reporter: tonight in delaware, history was made in a near empty high school gymnasium. joe biden introducing his running mate, noting she's like none who have come before her. >> as a child of immigrants, she knows personally how immigrant families enrich our country, as

well as the challenges of what it means to grow up black and indian-american in the united states of america. her story is america's story. >> reporter: biden promising senator kamala harris will inspire a new generation. >> this morning, all across the nation, little girls woke up, especially little black and brown girls, who so often feel overlooked and undervalued in their communities. but today -- today, just maybe, they're seeing themselves for the first time in a new way. as the stuff of president and vice presidents. >> reporter: biden coming to harris's defense, seizing on president trump's attacks on his running mate. >> donald trump has already started his attacks, calling kamala, quote, "nasty." whining about how she's, quote, "mean" to his appointees. it's no surprise, because whining is what donald trump does best.

better than any president in american history. is anyone surprised donald trump has a problem with a strong woman or strong women across the board? >> reporter: biden painted his one-time rival as a member of the family, citing her friendship with his late son, beau. >> kamala, you've been an honorary biden for quite some time. i know how much beau respected kamala and her work, and that mattered a lot to me, to be honest with you, as i made this decision. >> reporter: harris also paying tribute to her late friend. >> ever since i received joe's call, i've been thinking, yes, about the first biden that i really came to know. and that, of course, is joe's beloved son, one of his beloved sons, beau. and let me just tell you about beau biden. i learned quickly that beau was the kind of guy who inspired people to be a better version of themselves.

he really was the best of us. and when i would ask him, "where did you get that? where did this come from?" he'd always talk about his dad. and i will tell you, the love that they shared was incredible to watch. it was the most beautiful display of the love between a father and a son. >> reporter: harris says she's been inspired by the essential workers -- from doctors to truckers -- who've stepped up during the pandemic. >> but whenever i think that there is a reason for doubt, whenever i've had my own doubts, i think of you, the american people, the doctors and nurses and front line workers who are risking your lives to save others. >> reporter: the former prosecutor then taking direct aim at the president. >> the case against donald trump

and mike pence is open and shut. this is what happens when we elect a guy who just isn't up for the job. our country ends up in tatters. and so does our reputation around the world. >> mary bruce with us live tonight from wilmington, delaware. and mary, joe biden also taking note today that today marks the third anniversary of the white supremacist rally in charlottesville and it was clear not only in his words today, but in his choice of a running mate, the message he's sending to the country. >> reporter: david, joe biden has said that president trump's response to charlottesville is what inspired him to run. that he simply couldn't stand by after president trump said there were very fine people on both sides. and tonight, biden said he is proud to have harris by his side in this battle, saying she, quote, knows what's at stake. david? >> mary bruce leading us off again tonight. mary, thank you. president trump before the cameras at the white house just a short time after joe biden and kamala harris spoke. in a new interview today, he had

already called kamala harris a disaster, labeling biden and harris as socialists. and tonight, what the president again said about suburban housewives here in the u.s. here's our chief white house correspondent jonathan karl tonight. >> reporter: just two weeks ago, donald trump said kamala harris would be a, quote, "fine choice" to be joe biden's running mate. today, he called her a disaster. >> she is a disaster, she's going to be a disaster, i think, for their party. >> reporter: and, in an indication of how he's likely to take on biden and harris as the campaign goes forward, he called both of them socialists. >> i heard, actually, she's the most liberal person in all of congress. that's what i've heard. more liberal than bernie sanders, believe it or not. >> reporter: so far, team trump has been all over the map in their attacks on harris. a republican party spokeswoman, for example, tweeted harris is, quote, "completely controlled by the radical left." but an rnc press release then declared "liberals" are in

"revolt" over biden's choice. on a call with reporters, trump surrogates called harris, who is a former district attorney, both too soft on criminals and also too tough. >> i don't want someone who says that they are not going to be tough on hardened criminals. >> reporter: minutes later -- >> she fought to keep inmates locked up in overcrowded prisons. >> reporter: and as biden welcomes the first black woman to a major party's presidential ticket, president trump is now publicly embracing a republican candidate for congress from georgia with a history of making racist, anti-semitic and anti-muslim statements. marjorie taylor greene is also an outspoken supporter of the baseless q-anon conspiracy theory that the president is fighting a so-called deep state in what she calls a "global cabal of satan-worshipping pedophiles." greene declared victory last night with these words about house speaker nancy pelosi. >> she's an anti-american, and we're going to kick that [ bleep ] out of congress.

>> reporter: and today, the president tweeted that greene was, quote, "a future republican star" and "a real winner." >> so, let's get right to jon karl with us live in washington tonight. jon, the president knows he needs women voters this fall and today, he tweeted a message, saying, "the suburban housewife will be voting for me." >> reporter: david, he's attempting to appeal to suburban voters, a key swing group, by playing on racial fears. here's the actual tweet. he tweeted, "the suburban housewife will be voting for me. they want safety and are thrilled that i ended the long-running program where low income housing would invade their neighborhood." but david, it's not clear how many modern american women will respond to this racially charged appeal to, quote, suburban housewives. >> jon karl tonight. thank you, jon. and all of this amid a new and dire warning about masks in this country. troubling new signs of a possible resurgence in some of america's largest cities, including baltimore, chicago and

boston. and a growing risk in college towns this fall. and the numbers tonight. 24 states still seeing deaths on the rise. more than 165,000 lives lost. tonight here, the worries over schools. how to open safely. a second high school in georgia closing for two weeks now, nearly 1,200 students and staff in that district alone are now in quarantine already. and tonight, new and strong words from the head of the cdc about wearing masks. saying he is not asking some to wear them, that we all have to. or that this fall could be the worst we've ever seen. here's abc's matt gutman. >> reporter: in arizona, a state battered by the virus, parents and students demanding in-person classes. >> only when it's safe! >> then don't get paid at all! >> they're teachers. this is their job. and this is what they need to be here to do. >> reporter: but teacher brad outhrietngs diabetes and worries covid.

>> feel like, in a w, they've made us enemies. >> reporter: and he's calling it quits. >> i've resigned as of >> reporter: in boerne, texas, it was the first day back to school. students separated by plexiglass and all teachers and students required to wear masks. but in cherokee county, georgia, nearly 1,200 students and staff are quarantined after dozens tested positive. two high schools now closing for two weeks. another georgia high school, where these images of students without masks ignited a heated debate, now has 35 people testing positive. students protesting a school board decision to switch to partial online learning. >> we shouldn't be forced to go online because others are fearful. >> reporter: and tonight, the cdc director urging every american to wear a mask. >> i'm not asking some of america to do it. we all got to do it. >> reporter: warning of the consequences. >> if we don't do that, as i said last april, this could be the worst fall, from a public health perspective, we've ever had. >> reporter: when david asked dr. fauci about those images of students without masks -- >> there should be universal wearing of masks. when i see sights like that, it

is disturbing to me. >> reporter: new cases down in 49 states. in california, one hospital system taking matters into its own hands. because sending tests to outside labs can take so long to get results, hospitals like this one, providence st. joseph, have spent enormous resources on obtaining machines like this, which can process up to 900 covid tests every day, all of it in-house. but tonight, a new model predicting places like chicago, baltimore and boston could be emerging covid hot spots in the fall. >> this virus is still here and very much present. and that's our reality. >> reporter: in new york, police now investigating after this video emerged a group of young people taking over a city bus, turning it into a party. no masks in sight. across the river in new jersey, where the governor called for schools to reopen, but hundreds of teachers refused to return to the classroom, tonight, the governor relenting, allowing schools the option of going all virtual.

>> there is no one size fits all plan to this very difficult situation. >> reporter: david, here in california, hospitalizations are down 20%, prompting the governor to proclaim that the state has turned the corner on the pandemic, but they're not quite ready to open up all schools like the one behind me yet. that with a 150% increase of covid cases in children and teens just over the last month. david? >> all right, matt gutman. great to have you with us tonight. matt, thank you. and you heard that urgent warning from the head of the cdc about wearing masks. well today, a sheriff in florida ordering deputies not to wear masks. and tonight here, a new study. researchers in the lab, putting all different kinds of masks to the test. so, which ones do they believe work best and which ones do little, if nothing at all? here's abc's marcus moore with the results. >> reporter: tonight, as more businesses and local governments are requiring masks, one florida sheriff is banning them. marion county sheriff billy

woods is prohibiting his deputies from wearing masks at work and visitors to the sheriff's office, too. while there are exceptions, including jails, hospitals or dealing with suspected covid patients, the sheriff says the policy is to "ensure there is clear communication and for identification purposes." the move comes after the county's largest town, ocala, recently passed a mandate, but the mayor vetoed it. the cdc says face masks -- which stop droplets of saliva -- are a front line defense against the spread of covid-19. researchers from duke university used lasers to better visualize how well different masks stop those droplets. >> surgical mask, trial one. go. >> stay healthy, people. >> reporter: the more particles visible in the light, the less effective the mask. though they only ran the test once, their study found the fitted n-95 mask, the surgical mask and the poly-cotton mask did best. >> this one here is fleece. you see lots of little particles. >> reporter: researchers said the fleece gaiter they tested actually resulted in tinier particles being released than

speaking without a mask. >> these little droplets could be problematic, because they have an easier time being carried away by air. >> reporter: but experts don't know whether tiny droplets necessarily increase the chance of transmitting the virus. david, it's important to stress that this was a limited study. researchers still don't know what size or how many particles it takes to make someone sick. the bottom line is health experts agree, any mask is better than no mask. david? >> all right, marcus moore tonight. marcus, thank you. and we take note of an image coming in from overseas tonight. a deadly train derailment near the northeastern scottish coast. take a look. aerial images coming in showing several train cars off the tracksndenofir responders at the crash site. at least three people were killed, including the driver. six others were hospitalized. the cause is under investigation tonight. there was heavy rain in the region that had disrupted train service. back here at home tonight, and there is news again this evening on college football and the fall season amid this pandemic. the big 12 announcing it will move forward. here's kaylee hartung again tonight.

>> reporter: tonight, the pendulum swinging in favor of college sports returning to action. the big 12 conference committing to play and releasing an updated football schedule. the commissioner bob bowlsby saying, "we are comfortable in our institutions' ability to provide a structured training environment, rigorous testing and surveillance, hospital-quality sanitation and mitigation practices that optimize the health and safety of our student athletes." this, a day after the big ten and pac-12 canceled all fall sports. their medical experts warning of the potential long-term effects of covid-19. but the remaining three members of the power five conferences now say they have the protocols in place to protect their athletes and they'll proceed with caution. >> canceling football will not cancel their risk of getting the virus. they're still going to go to school. they're still going to go back home and visit with their family. they're still going to be social. >> reporter: david, the soonest we could see college football played is four weeks from now. still up for debate whether we'll see fans in these stadiums. david?

>> kaylee hartung from baton rouge again tonight. thank you, kaylee. and when we come back on the news tonight, an air force helicopter shot in the air over virginia. the fbi now investigating tonight. life is full of make or break moments. that's why it's so important to help reduce your risk of fracture with prolia®. only prolia® is proven to help strengthen and protect bones from fracture with 1 shot every 6 months. do not take prolia® if you have low blood calcium, are pregnant, are allergic to it, or take xgeva®. serious allergic reactions like low blood pressure, trouble breathing, throat tightness, face, lip or tongue swelling, rash, itching or hives have happened. tell your doctor about dental problems, as severe jaw bone problems may happen. or new or unusual pain in your hip, groin, or thigh, as unusual thigh bone fractures have occurred. speak to your doctor before stopping, skipping or delaying prolia®,

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another busy night of news. for the first time, we saw joe biden and kamala harris together today at a school gym, late today in wilmington, delaware, walking out in masks, keeping a distance. joe biden saying her story is america's story. harris saying america is crying out for leadership. president trump at this hour describing harris as angry and also talking about what he considers her mistreatment at the time supreme court nominee brett kavanaugh. the questioning of kavanaugh. 83 days to go, some of the lines of attack on both sides taking shape. good night.

how long it will take to create a safe and effective coronavirus vaccine. >> i'm cornell bernard at san quentin. local health officials say early warnings that a covid outbreak inside the prison were largely ignored by officials. that story is coming up. >> let me introduce to you, for the first time, your next vice president of the united states, kamala harris. >> can california senator help democrats win the white house? the team effort starts now. >> in just 83 days, we have a chance to choose a better future for our country. >> the countdown is on in an yemtd election year set against

the back drop of the coronavirus. >> thank you for yoing us. . joe biden and kamala harris held their first joined event unlike anything we've witness in the politics. there were no cheering crowds, no crowds at all because of coronavirus and the pandemic is political. >> the pandemic really has given a whole new look to political campaigns, has not it? it was biden's first campaign event in five months. the official start of this official campaign included a shout out to oakland. >> reporter: wearing matching black masts in a crowded high school gymnasium, they appeared together for the first time