area is right up there too. >> that's amazing. 20 years. nbc "nightly news" is next. and we'll see you back here at 6:00. deadliest day in afghanistan. 30 americans killed, many of them elite navy s.e.a.l.s. the most devastating attack for u.s. troops since the start of the war in afghanistan. tonight, reports from the region and here at home. downgraded. the u.s. loses its perfect credit rating for the first time in history. what does it mean for the global economy already in turmoil and for your bottom line? and american graffiti. one man's trash is now another man's treasure. the changing landscape of a modern art form. captions paid for by nbc-universal television

good evening. after ten years of war, today will sadly be remembered as the single deadliest day for american forces in afghanistan. the pentagon confirms that 30 u.s. troops, 7 afghan troops and an afghan interpreter were killed when their helicopter was shot down responding to assist other troops caught in a firefight with the taliban. the dead include 22 navy s.e.a.l.s, some of them members of the legendary s.e.a.l. team 6, the unit credited with the killing of osama bin laden in pakistan earlier this year. the horrible news comes at the end of a week in which those back home were focused on knt's debt, falling stock prices and partisan squabbling. >> now this brute's reminder, we are still a knt at war with 98,000 american troops putting their lives on the line i afghanistan every day. we begin our coverage from our kabul base and atia abawi.

good evening. >> reporter: good evening, lester. the taliban quickly claimed responsibility for today's attack stating that its fighters shot down the helicopter with a rocket. the american and afghan special forces were working side-by-side when their operation took a deadly turn. a senior american official says the team was on its way to a mission not far from kabul in wardak province. a site known for strong taliban presence. their target, a target housing insurgent fighters. the ch-37 chinook helicopter came und are fire and crashed killing everyone onboard. in operations like this one, helicopters can be especially vulnerable. >> this helicopter like any helicopter, you go pretty fast in a straight line, but when it is over a target area, when it is inserting itself into a target area, it is slow, and it

is a very, very easy target for troops on the ground. >> reporter: the 38 people killed included 22 u.s. navy s.e.a.l.s, 5 army aircrew men, 3 air force airmen and as well as 7 afghan special forces and one afghan field dog was also killed. the navy s.e.a.l.s were from at least two different units and included some from unit 6, credited with killing bin laden back in may. none reported to be part of the bin laden operation. president obama expressed condolences to those killed. their deaths, he said in a statement, a a reminder of the extraordinary sacrifices bade my our military and their families including all who served in afghanistan. as the united states draws down its presence in the country, the special forces are expected to become even more important. >> the president of the united states says we're leaving afghanistan and indeed we have

begun to leave, and what are we going to leave behind ask we're going to leave behind special operations forces. >> reporter: although nato deaths decreased slightly this year in afghanistan, this latest attack demonstrates just how dangerous the country remain. even for the most elite american and afghan forces. both u.s. and nato officials continue to investigate just what went wrong and how today became the most devastating day for american troops in afghanistan. lester? >> atia abawi in afghanistan. joined by four-star general and decorated impact general barry mccaffrey. it's easy to forget this is a relatively small community. besides the deep personal loss, will this affect the u.s. war tempo? >> probably not, lester. it reminds all of our viewers we've had 15,000 killed and wounded in afghanistan. it's a big operation.

the casualties increased each year, and the special operations community has carried a tremendous burden of that combat operation. a lot of these rangers, sergeants, delta s.e.a.l.s, 160th aviation on their fourth, sixth combat tours. it's a tremendous struggle to keep this up. i think there'll continue. >> we continue the drawdown. will rangers and delta force be among the last to leave? >> i would think so. the absolutely last out, trainers trying to develop the afghan army and police right up to the very end, but clearly what we're facing is a political challenge here in the united states in which increasingly there is little support for this war. maybe two-thirds of the american people, a $10 billion a month operation. we've got 100,000 troops still on the ground. it's a very tough dilemma to support this operation going forward.

>> last question. how much of a psychological victory is this for the taliban? >> well i think they'll try and make make a lot of it, but you know, we've got to remind ourselves that, in fact, in the last year there have been significant tactical successes against the taliban. they are not winning. security is spreading. roads are opening. schools are opening. the question is, one of time. what will it look like in 2014? >> general barry mccaffrey, our thanks for joining us tonight. despite our fascination over their work, navy s.e.a.l.s shunned publicity and as a war don't tell war stories. still in the tight-knit stateside communities where they're based, everyone has an idea what these quiet heroes are about and the extraordinary dangers they face. tonight those communities feel a deep sense of loss. miguel almaguer has the latest.

>> reporter: tonightance as you mentioned, this is where loss is being felt. in coronado, california, where the navy s.e.a.l.s train, sorrow and grief. >> it was devastating. absolutely devastating. had i first heard it i wondered if maybe it wasn't a retaliation if they were aware who was onboard the helicopter. >> it took me a while to sink in. then when it did i felt like i was melting. i didn't know what to say or do. >> reporter: with 30 american troops killed in afghanistan today, 22 belong to one family. the navy s.e.a.l.s. >> go! >> reporter: they are the best of the best. special operations teams so elite, 80% of those who begin training doethts make the cut. >> we like when it cuts. >> reporter: the navy pushes the s.e.a.l.s beyond the limit. mental toughness, physical fitness and extreme courage, not just requirements for the job but a way of life. >> you can always counted on the navy s.e.a.l.s and special

forces to do the hard jobs. >> reporter: the s.e.a.l.s endure more than 30 months of brutal and specialized training, taught to react quickly in dark environments. plunge from a plane, even for combat under water. they are prepared for anything able to deploy anywhere. >> they work in the shadows and the sooner they can step back in the shadows the happier they are. >> reporter: retired colonel was a navy s.e.a.l. and served nearly three decades with the military. >> these young men are national treasures. they're irreplaceable. you don't find them everywhere. so this is -- this was a tragedy for the entire country. >> reporter: the s.e.a.l.s are known as silent warriors but their mission, like the killing of osama bin laden, made a clear statement. a group that is takes the ultimate price. >> my nephew is over there. anytime you hear of any mass killings it brings it home and makes me a little nervous about what's going on.

>> reporter: a community used to war, but one that's never suffered a loss like this. while the navy s.e.a.l.s have trained here for years, this region is also home to other military branches, and tonight, lester, they, too, were mourning the loss of their troops. >> miguel almaguer, thank you. now to the other big story we're following. the unprecedented downgrading of the u.s. credit rating. standard & poor's one of the agencies that rates credit risks dropped the u.s. from a aaa rating to a aa plus rating. despite congress agreeing on a plan to cut the deficit, s&p has said it's not enough. cnbc's chief washington correspondent john harwood is with us from the white house now to tell us more. john? >> reporter: after a week of turmoil in politics and financial markets, lester, late friday brought the shock no one wanted. a major rating agency saying u.s. debt was no longer the safest in the world. as a bitter debate unfolded in

washington ober debt and potential default, warning that the white house and congress needed a $4 trillion deficit reduction plan to keep a aaa rating, but in the final hours, republicans and democrats struck a deal just over half that size. late friday, standard & poor's, one of three major rating agencies, followed through, lowering its u.s. long-term credit rating one notch to aa plus. s&p said last night, the political brinksmanship of recent months highlights what we see as america's governance and policymaking becoming less stable, less effective and less predictable.cc1: harsh reactions came quickly. china a major creditor said the u.s. must cure its addiction to debt. the obama administration officials were furious at s&p saying the agency initially miscalculated america's debt levels. treasury officials point out moody's and fitch, the two other major agencies are keeping the u.s. rating at aaa.

the credibility of the entire industry suffered in the financial crisis three years ago. >> given s&p's track record and rating1: agencies going into the financial crisis, missing subprime mortgages, a real question whether investors are going to give significant credibility to this downgrade. >> reporter: president obama himself pointed out the same saying we freed to need to do b >> both parties have to work nations to get ourcc1: financial problems in order. >> reporter: this isn't a sure bet. >> what works over the long term may not work in the short term. that's the problem. to a politician, the long term is two years. >> hopefully the question for voters, can i look ahead and see that things are going to get better or am i looking ahead and seeing things getting worse? >> reporter: with europe facing a full debt problem what it all means for the global economy. of course, washington gets another chance to impress

ratings agency s when a special committee of congress seeks to specify $1.5 trillion in spendispend reductions this fall. lester? >> john harwood, thank you. as if the struggling economy isn't bad enough, this downgrade news forcc1: your family's bottom line. our report from nbc's john yang. >> reporter: dan gunning has spent a year looking for his florida retirement home. today he decided he needs to find it fast.cc1: worried that interest rates will go up now that the united states credit rating has gone down. >> i don't have the luxury of time anymore, if interest rates are going to go up. >> reporter: analysts say the downgrade to demand higher interest rates for u.s. bonds. that would raise consumer interest rates for everything from credit cards, student oans, car loans and homecc1: mortgages. a little increase can mean a lot. on a $ 200,00030-year fixed mortga mortgage, a half point hike, an extra $740 a year.

this realtor worries what that would do to business. >> in the market, it scares me. everybody's very, very cautious. >> reporter: that's all in theory. uncertain.pact iscc1: much depends on how global investors react starting in the asian markets. the first to open since the downgrade. >> if this effectively tloep throws gasoline on the fire and asian markets sell off sharply it's likely we'll have a difficult time here in our markets monday morning. > reporter: more psychological practical further shaking america's confidence in the economy. that could be a knockout blow to the struggling economy. >> how much worse can it get? >> heads for hard times regardless of what happens. >> reporter: experts have advice for investors and consumer. >> the last thing you want to do hit the panic button altogether nap will kill off confidence for consumers and businesses alike. >> reporter: advice that's been increasingly hard to follow in turmoil. of financialcc1:

john yang, nbc news, new york. we will have much more on the tragedy in afghanistan and the economy tomorrow morning on "meet the press." senators kerry and mccain are among david gregory's guests. when "nightly news" continues this saturday, our own richard engel in africa on the ground for what could be a turning point in the effort to feed the starving. and later -- decay, now of urban cc1: a bright spot in the neighborhood, and going for top dollar. cc1:cc1:cc1:cc1:cc1:cc1:: :

cc1: we want to show you dramatic pictures out of london where hundreds of people have gathered to protest the death of a young father reportedly killed by police. the march through the streets urned violent with protesterscc setting storefronts and1: bus on ce cars and acc1: fire. for millions of people starving in the heart of africa, a stunning development today in the first ray of hope in months. islamist rebels who had been blocking desperately needed aid deliveries appear to have pulled out of the somali capital of mogadishu. could be a turning point. our chief foreign correspondent richard engel is there. >> reporter: at a health clinic in mogadishu, it's hard to see

how malnourished miriam is until takes off her cc1: shirt. she weighs only 9 pounds. little more than when she was born 2 1/2 years ago, but she's getting better. she can drink from a bottle and keep the liquids down, but at this clinic, everything has to be seen today. militants unexpectedly left mogadishu overnight. violent years, acc1: accomplish sa called al shabaab has been hated here. it banned music and gold and imposed harsh islamic law, but when they banned foreign food relief it was too much for this woman. she lost two of her children to the famine. al shabaab denied food access to our region. shecc1: said.or that, africankeepers were stunned to out of the city.1:

they could do suicide attack, but the prime minister told me it's nonetheless a victory for his government which yesterday only controlled half of mogadishu. >> i think they left our city because they lost the fight. >> reporter: we traveled by convoy with the african peacekeepers through newly taken land, to the old soccer stadium. this was the main al shabaab training camp in mogadishu. xplosive, snipers, where thecc: militants made almost all of their videos. now al shabaab has left. finally, in somalia, this won't: stop, but denying food to starving people may have cost them a key stronghold in mogadishu that could be difficult to take back. engel, nbc news, mowing douche schoo. many have beensking how we've compiled a list of charities. it lookede come back,cc1: like the coast is clear, but is

trouble brewing once again in the tropics? cc1:

the answer to all your problems is in this little bottle. this contains vitamins, meat, vegetables and minerals. >> we still love lucy and she's still makes us laugh all these years later. a lot of people reminiscing about lucille ball today, what would have been her 100th birthday. even the folks at google are showing some love with a google doodle of the vintage tv on the home nachplays classic "i love lucy "clips. turning now to severe weather across the country in parts of north carolina, flash floods wash into several buildings, prompting evacuations. in one part of the state, more

more than 4 1/2 inches of rain fell in just six hour, and the sweltering temperatures continue across much of the south, all or part of 17 states are under an excessive heat warning or advisory. for a closer look at the extreme heat with turn to the weather channel's samantha mohr. >> good evening, lester. yes, the heat has been incredible. in fact, we have seen four times the number of triple digit days than we would see in an average year. that means 44 days above 100 so far in oklahoma city. so this is really creating a streak in dallas-ft. worth, as well. the record to beat is 42 days of 100 in a row and we've seen that at 36. so with the next week we'll likely have a new record in dallas-ft. worth, and 13 of these days have been over 105 degrees. so 13 days of 105 or hotter. this follows one of the warmest monthen or record in washington, d.c., philly and baltimore. the heat is on here and it is

not letting up across the nation. a big ridge of high pressure in place creating triple digits across much of the plain states and no relief in sight and the streak continues here. and guess what? down, but not out. emily is stirring up once again. now as a depression, so we'll watch her rain as it comes into florida, lester. >> samantha, thank you. up next, american graffiti moving in doors and selling for big bucks. cc1:

finally tonight, the changing landscape of american graffiti. modern graffiti has been around for decades on everything from highway signs to dumpsters, but recently it's become a hot commodity in the art world museums and selling for big bucks.cc1: that's prompting some to wonder where to draw the line on one man's vandalism and another expression.tic cc1: here's nbc's lee cowan. >> i have an active case on him: >> reporter: when lapd detective

victor became a cop, he nerve thought he'd end up an art critic. >> you can see the gra teaty. >> reporter: but as a member of the l.a. graffiti tasks for, he now polices the vast canvas that is the inner city.cc1: >> there have been some cases made out of fingerprints. >> off the cans. >> reporter: to him, it is vandalism, even if sometimes, it's a tough call. >> it is art, but the difference is permission. >> reporter: last year, 35 million feet of graffiti were painted over. that's an 8% jump over the year before that. as you can see, just keeping up is no easy task. and it's not just los angeles. cities all around the country are seeing graffiti surge. places like florence, alabama, and the state house in tennessee. >> when you see it making its way into important museums, that gives you an idea of how big it is.cc1: >> reporter: at this gallery in sunset marquise hotel in west hollywood, graffiti is big business. >> that's $9,000?

>> $9,000. >> reporter: cope two as the artist is known, started years ago. by tagging subway cars in new york city. now, he's an artist known the world over. it's a hit in hollywood, too. the recent documentary by banksy, was nominated for an academy award. even the los angeles museum of contemporary art has given graffiti a lofty platform. >> some people say it has to be illegal to be graffiti. i don't really agree with that. >> reporter: this man is a curator of the venice art walls. he offers a legal place for street artists to create. >> i was told at a young age, art will not get you nowhere. guess what? i travel. i do shows. i sell paintings.cc1: >> reporter: critics say this attention is just glorifying the crime. but it's the canvas that's the controversy. not the spray strokes themselves. lee cowan, nbc news, venice beach, california. that's "nbc nightly news" for this saturday. i'm lester holt. reporting from new york.

i'll see you tomorrow morning on "today," then right back here tomorrow evening. good night. -- captions by vitac -- www.vitac.com good saturday evening, i'm diane dwyer. the coast guard is asking for the public's help tonight in finding a