down to the wire. the heat is on as the candidates swing away. the final 48 hours in florida and tonight, big changes in our new poll. deadly pileup. drivers blinded by smoke. a massive highway crash. and tonight, questions about why the road was open. nuclear tensions. inspectors arrive in secretive iran. a critical mission as the war of words with the west takes a dramatic turn. and, heart of the matter. ground-breaking health news tonight. what doctors are saying about the choices you make early in life and their impact later on. captions paid for by nbc-universal television the bruising fight to win

tuesday's republican presidential primary in florida has turned into a spectator sport. with less than two days to go the language, characterizations and accusations being traded back and forth between mitt romney and newt gingrich have reached a new level of harshness and it's fueling volatility entering the final stretch. romney's renewed aggressiveness may be paying off. he's moving up and leading gingrich by 15 points. in a state that four years ago went with the eventual republican nominee. our political team is in place to cover it all. peter alexander is in pompano beach to lead it off. >> reporter: the bitter feud between mitt romney and newt gingrich continued tonight. even as romney goes on the offensive against gingrich, the romney campaign is saying that it's trying to dismiss gingrich's attack on romney's character, calling them both desperate and over the line.

with strong poll numbers showing him in the driver's seat, mitt romney didn't let off the gas. at the largest rally of his entire campaign. >> he's now finding excuses everywhere he can. going from station to station, complaining about what he thinks were the reasons he's had difficulty here in florida. but we've got a president who has a lot of excuses and the excuses are over. it's time to produce. >> reporter: this morning, den give once again challenged romney's honesty. >> this is a smart man, as you point out, he was well-coached. he came into the debate prepared to say things that were false. >> reporter: later calling himself the legitimate heir to the reagan movement toughened his stance. >> i just think it will be very, very clear and increasingly clear over the next few weeks that this party not going to nominate somebody who is a pro-abortion, pro-gun control, pro-tax increase liberal. >> reporter: gingrich's confrontation with the

republican establishment got a boost from sarah palin this weekend who called on voters to defiantly play the role of spoiler. >> so, if for no other reason, rage against the machine, vote for newt. annoy a liberal, vote newt. >> reporter: herman cain, who fire the up the tea party with his 9-9-9 tax proposal, endorsed gingrich saturday night. >> because gingrich is not afraid of bold ideas. and i also know that speaker gingrich is running for president and going through this sausage grinder, i know what this sausage grinder is all about. >> reporter: after campaigning this weekend in maine, ron paul today argued he's the best candidate to represent fr frustrated voters. >> enough, who's beniche, who'ss all these years and the insider, claiming he's leading the tea

party, to me that's strange. >> reporter: the miami herald wrote, mr. gingrich might be the feistier candidate but if republicans care about elect ability in november mr. romney is the better choice. rick santorum's oldest daughter took his place while santorum left the trail to be with his 3-year-old daughter bella, who suffered from a rare genetic disorder and is hospitalized this weekend. >> family comes first and he's being a dad and a husband right now. >> reporter: while there's one more full day left to go, more than 460,000 floridians have cast their ballots either by absentee or early voting. >> all right, peter, thank you. the florida primary will be an early test of republican strength among the nation's fast-growing latino population. the gop candidates have been paying special attention to latino voters in florida, knowing their support both now and in november could hold one of the keys to the white house.

nebraska's ron allen picks up our coverage. ♪ >> reporter: in florida the campaign has a distinctive latin beat. [ speaking spanish ] >> reporter: an aggressive push to court the state's fastest-growing electorate. latino voters. now more than 13% in florida. important in the gop primary and probably even more crucial in november. is this vote in the left hand election going to swing the tide one way or the other? >> florida's always a close state, and yes, it can. >> reporter: patrick publishes a 90-year-old multi-lingual newspaper in tampa. it's a lot more complicated than it used to be? >> absolutely, and florida especially we have a mix of cubans, puerto ricans, mexicans, venezuelans, colombians. >> reporter: cuban conservative republicans used to dominate, galvanized by tough anti-castro policies. however, a big influx from

places like puerto rico, american citizens who tend to support democrats. >> who do you like? >> i like obama. >> do you think you'll always vote democrat? >> yes, i think, till now. >> reporter: president obama won the latino vote 2-1. then, latino voters helped sent republican marco rubio to the u.s. senate. >> the biggest priority right now should be jobs. >> reporter: latinos also have a generational divide. adrian mar 10 knees and his wife are republicans. their daughter prefers democrats. their son emmanuel -- >> republican, democrat, independent? >> independent. >> reporter: right down the middle. not listen to your grandparents, not listen to your mother. >> nope. >> reporter: what's the candidate to do? >> they need to realize that they can't just come up with a quick sound bite and get hispanics in the state of florida. >> reporter: for every vote often counts. down to the wire, a race for latino voters wielding

increasing political clout. ron allen, nbc news, tampa. >> our political director and chief white house correspondent chuck todd joins me from our washington news room. it seems gingrich and romney see the path to the nomination is on this question of elect ability. who can face down barack obama in the general election. is that's what's driving this increasingly heated rhetoric we're hearing? >> it seems to be driving romney's numbers up. the number one issue, quality in our poll, elect ability. romney had even a bigger lead on gingrich on that one. yes, electability is driving this a little bit, particularly in florida. these big, larger states, unlike iowa and new hampshire, south carolina, where you get more of a chance to know niece candidates, in florida it's all about tv ads. that's been another advantage for romney. he's carpet-bombed the state in a way you can tell it's gotten under gingrich's skin. the question i have, lester, what does gingrich do after florida if he indeed does lose?

because there's an awful lot of space and time before he can get to a state that he has a good chance of winning. >> we've seen the stop gingrich movement among mainline republicans. at the same time, tea party movements seem to be circling the wagons around gingrich. are we moving up to a day of reckoning in the republican party here? >> reporter: not yet but i establishment really is nervous about this issue of romney not having more time to basically fix his general election problems. this process is not been good to him. he is upside down in his personal rating. a net negative right now. that's not good. he needs time to fuks that. gingrich clearly isn't going away. what we saw in new hampshire, sort of the revenge of the tea better and the anti-establishment, rallying around newt, don't be surprise tuesday me see that again. this thing is destined to go at least until mid-march. you've got southern primaries and gingrich is going to want to see if he can get some momentum back there and that's where i think the data party's going to try to carry him through.

we'll see. >> chuck todd in our washington news room, thanks. >> tonight a stretch of i-75 remains closed in florida. 15 hours after a deadly pileup this morning. cars, trucks and tractor-trailers collided in a mangled mess as a brush fire raged nearby. blinded by haze and smoke, rescuers rushed to help as crashes continued to happen all around them. tonight there are questions about why that stretch of highway was open in the first place. we get our record from nbc's lilja luciano. >> reporter: it's hard to tell from the cluster of these blurnt-out shells how many vehicles came crashing together on florida's interstate 75 north of orlando early this morning. witnesses describe the scene as looking like it was the end of the world. police say at least ten people are dead and some 20 others injured after a blinding mix of heavy fog and thick smoke from a nearby brush fire blew across the highway, reducing visibility and causing havoc on both north and southbound sides of the

highway. >> smoke and fog settled over the area quickly and dismated the visibility. >> reporter: highway patrol officials say they closed the road earlier but reopened it deciding visibility had improved enough and traffic was light at the time. not long after the deadly collisions began. thes started around 3:45 in the morning. when rescuers arrived police say visibility was so poor they could only find the victims by following their screams for help. officials say there were seven tractor-trailers and at least 12 passenger vehicles involved in the pileup. rescue crews were still removing bodies from the site well into the afternoon. peeling off the tops of cars to extract trapped victims. nearly 15 miles of i-75, the interstate that runs north to south on the western side of florida, remained closed throughout the day as investigators worked the scene. authorities say the brush fire that started saturday afternoon was not natural and could have been intentionally set. lilja luciano, nbc news, miami. tonight the mayor of oakland, california, is busy

assessing the damage after dozens of occupy protesters stormed city hall, smashing displays and spraying graffiti after a day of clashes between police and protesters. more than 400 were arrested. tonight amid rising tensions and threats related to iran's nuclear ambitions a team of international inspectors have arrived there. >> good evening, lester. in a rare visit to iran, a senior delegation of iaea inspectors began an important three-day visit that could influence washington's next move. their purpose, to determine whether iran has a secret nuclear weapons program. tehran maintains that its program is purely for civilian purposes. it's still unclear whether the delegation will be allowed to visit nuclear facilities or just hold talks with iranian officials.

allowing in the iaea delegation and comments by president ahmadinejad earlier this week that iran was willing to restart nuclear negotiations seemed to be a sign iran was striking a more conciliatory notes. western powers call this a stalling tactic. iran's speaker of the parliament warned the iaea team to be professional or suffer the consequences. tensions with the west were ratcheted up even further this month when washington and the eu imposed their harshest sanctions on iran so far. in response to those sanctions, iran's parliament announced that it was considering retaliation with a preemptive ban on oil exports to the eu. iran's oil minister announced iran would stop selling oil to some countries which could send oil prices sky high and leave some european countries scrambling for an alternative

oil source. lester? in syria there are reports more than 60 people have been killed by government forces in the last 24 hours. that's in addition to more than 100 deaths since thursday, marking the bloodiest stretch in syrian's ten-month-long uprising. yesterday arab league observers suspended their monitoring mission in the country saying it's too dangerous to stay. there's word from italy it could be close to a year before they're able to remove that capsized cruise ship off the coast of tuscany. today bad weather continues to haver recovery efforts for the 17 still missing aboard and rough seas of that delayed an operation to remove 500,000 gallons of fuel from the ship. big news tonight about heart health. a ground-proceeding look about choices we make their effects later in life. also reports about a major announcement in the works from facebook. business is booming on the late shift and restaurants

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internist, taking blood tests, put me on cholesterol medication and blood pressure medication. >> reporter: a ground-breaking new study from northwestern university shows how critical it is to start paying attention to heart health much earlier. almost everyone knows smoking, high blood pressure, high cholesterol and diabetes are the major risk factors for heart disease. the study revealed how extremely important they are, even at a relatively young age. for example, a 45-year-old man who has none of the risk factors has only a 1.7% lifetime chance of having a heart attack. if he has two or more risk factors, that number jumps to 42%. for a 45-year-old woman, the numbers are 1.6% with no risk factors, and 21.5% with two or more. >> this study is so important because it tells us even healthy appearing young individuals have a substantial lifetime risk for

cardiovascular disease if these risk factors are present. >> reporter: the study shows it is important to stay healthy. it found having no risk factors lowered danger substantiality at ages 55, 65, and 75 as well. but the biggest surprise was the great gauge for 45-year-olds. >> treatment started in the 40s can major a huge difference in their 70s or 80s. >> reporter: none of this means it's ever to late to start getting healthy. jim's risks are now well under control. >> i'm enjoying life. looking forward to it. >> reporter: the study proves the sooner treatment starts, the better the chances of avoiding heart disease into old age. robert bazell, nbc news, new york. when we come back here tonight, a major status update from facebook that has a lot of people talking. you wouldn't want your doctor doing your job. so why are you doing hers? only your doctor can determine if your persistent heartburn is actually something more serious...

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what a treat for a lot of americans who set their alarms for 3:00 in the morning. an epic final down under at the australian open. the reigning king of tennis did the again. novak djokovic gate rafael nadal in the longest grand slam singles final in the current era, 5 hours 33 minutes. djokovic has won four of the last five grand slams. "a sign of the times" tonight in hawaii. the nfl is relaxing its strict social media policy and allowing players to use twitter to interact with fans during the pro bowl in honolulu. there will be one designated computer on each sideline. no smartphones allowed. players will be tweeting with

the hash tag pro bowl. by the way, catch the game coming up next here on nbc. now to the news out of silicon valley that has a lot of people talking. reports that facebook is preparing for a major status update, a move that would vault the social networking giant into the ranks of the largest public companies in the world. john ford covers the tech industry for cnbc. he joins from us san jose to break down how big this deal could be. a lot of folks are going to want to get in on the ground floor of this. how big are we talking about? >> massive amounts of money here, lester. we're talking about in the neighborhood of $75 billion to $100 billion, potentially, more than i've got in my bank account. let's compare it to something. when google went public, it was a massive ipo around $23 billion. this is three to four times bigger, about the size at $100 billion of one mcdonald's, or half of a walmart. this is for a company, sure, almost everybody uses.

facebook, it's got 800 million active users, but few people know how they make money, through advertising and transactions. this takes facebook definitely to another level. >> end of the day we're still talking about an investment. you said 800 million users, it leads me to question how much more potential does this company have to grow? >> well, the interesting thing about facebook, yes, more than 800 million users at this point. some estimates have their reven revenue, their sales for last year, almost $4 billion. they're sort of just getting started. they've only start eed to reall figure out ways to get those people paying for things. if they can do that, there's a huge amount of potential here. 800 million, about half the people on the internet right now. >> amazing. john ford from san jose, thanks very much. up next, a lot of late-night cravings leading to a big change at the drive-through. it card. hey, aren't you... shhh. i'm researching a role.

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for everyone who loves it, and everyone who calls it home. finally tonight, a shift change at the drive-through that might just be a reflection of the nation's still-sluggish economy. in cities and towns across the country there's a customer base hungry for a late-night snack. these led to a spike in sales for fast food giants. they're taking notice, extending hours and staying up all night. that story from nbc's mike taibbi. >> reporter: taco bell's commercials talk about the toerth meal, available to 1:00 a.m. or later. >> who says nothing good happens after midnight? >> reporter: wendy's has been

aiming nocturnal hours to us. >> you can eat great even late. >> reporter: mcdonald's, mopping up at 10:30 in this gardenia, california, franchise, doesn't mean the work day's ending, just changing to the next shift. >> people are out and about, and they want us to be available when they are out and about. and thank goodness we can do that. >> reporter: the recession has been hard on the restaurant business. except in some markets. in the wee, small hour section, midnight to 5:00 a.m. >> traffic in restaurants during that period increased 4% over the last four hours. traffic overall has been down 3%. >> reporter: there's always been a segment of the workforce that wasn't strictly 9 to 5. casino workers, hospital staff, cops and emts refueling on the run. >> reporter: cub reporters working the newspaper's graveyard shift. i remember that guy. the night owl customer base has been growing. for mcdonald's and other major

fast food chains, the decision to extend their hours has to do with the way americans are working now. which for many in this tough economy means any way they can, at any hours they can. so mcdonald's now has 40% of its restaurants open 24 hours. up from 30% seven years ago. and others in the fast food world are following suit. >> it's here to stay and it's everywhere. >> reporter: an economy filled with people working night shifts, double shifts, second jobs. someone's got to feet them. mike taibbi, nbc news, gardenia, california. >> that's nbc nightly news for this sunday. brian williams will be here tomorrow. i'm lester holt reporting from new york. for all of us here at nbc news, good night.