By CHARLES BABINGTON, ASSOCIATED PRESSS

GREENVILLE, S.C. -- Barack Obama's re-election campaign kept up pressure against Republican rival Mitt Romney on two fronts Friday, launching a new ad defending the president's record on Medicare while challenging Romney to release at least five years of tax returns.

The TV advertisement - accusing Romney and running mate Paul Ryan of undermining the health care program critical to millions of seniors, came as Romney made plans to spend his time raising money in non-battleground states. That remains a top priority even with the election less than 12 weeks away and Obama making extended visits to toss-up states such as Iowa and Ohio.

Obama campaign manager Jim Messina made the tax-disclosure offer to Romney campaign manager Matt Rhoades in a letter Friday morning. Messina said he was taking the step because Romney "apparently fears the more he offers, the more our campaign will demand that he provide."Romney's wife, Ann, has repeatedly stated that concern in interviews, arguing that the more the couple releases, the more questions are asked.

Romney released his 2010 taxes and has pledged to release his 2011 returns. Messina said in letter that he wants Romney to provide three more years of returns.

Obama's campaign has questioned whether there are years when Romney paid no taxes. Romney defended his record Thursday, saying he has paid at least 13 percent of his income in federal taxes every year for the past decade.

"I did go back and look at my taxes and over the past 10 years I never paid less than 13 percent," Romney told reporters after he landed in South Carolina for a fundraising event Thursday. "I think the most recent year is 13.6 or something like that. So I paid taxes every single year."

Aides later said Romney meant to say 13.9 percent, the amount he already disclosed for his 2010 federal return.

On average, middle income families, those making from $50,000 to $75,000 a year, pay 12.8 percent of their income in federal taxes, according to the nonpartisan Joint Committee on Taxation. In 2010 and 2011, Romney made about $21 million a year.

Romney is able to keep his tax rate low because most of his income is from investments, which are generally taxed at a lower rate than wages. That type of legal tax figuring is something Obama has proposed changing, although his campaign notably said nothing about Romney's self-described tax rate itself.

In the new Medicare ad, Obama's campaign pointed to the AARP, an organization that represents senior citizens and which said in a letter to lawmakers earlier this year that Ryan's plan to transform Medicare into a voucher-like system would lead to higher costs for seniors.

The AARP said that Obama's approach would strengthen the program. Romney has criticized Obama for taking more than $700 billion in Medicare funds to help pay for the president's health care law.

Obama's campaign is running the ad in eight states: New Hampshire, Virginia, North Carolina, Florida, Ohio, Iowa, Colorado and Nevada.

This comes while Romney is campaigning in Alabama, South Carolina, Massachusetts and New York. He plans visits next week to Texas, Louisiana and New Mexico.

To be sure, Obama attends numerous fundraisers of his own. And Romney has spent significant time at public campaign events in swing states, and he will do so many times again before Nov. 6.

But the amount of time Romney is devoting to private fundraisers in noncompetitive states is notable. Even when he is in swing states, he sometimes attends only a fundraiser, without mingling with non-donors or appearing before local TV cameras, as he did Wednesday in Charlotte, N.C.

Romney is pouring time into fundraisers even though he has outdistanced Obama on that front for months. The former Massachusetts governor reported raising more than $101 million along with the Republican National Committee in July. Obama's campaign and Democratic National Committee raised $75 million for the month.

Romney's money advantage is expanded by technically independent groups flooding airwaves with ads criticizing Obama. Two pro-GOP super PACS - Restore Our Future and American Crossroads - have raised more than $122 million since the beginning of last year. Democratic-leaning groups Priorities USA Action and American Bridge 21st Century have raised about $30 million in that time.

Obama recently told voters, "Over the course of the next three months, the other side is going to spend more money than we have ever seen on ads that basically say the same thing you've been hearing for the past three months: The economy is not where it needs to be, and it's Obama's fault."

The candidate with the most money and TV ads doesn't necessarily win elections, and most polls suggest Obama holds a slight lead among voters. For now, at least, Romney's team has decided that pouring much of his time into fundraising is more valuable than another quick visit to Colorado, Florida or the other eight or 10 competitive states.

Romney, who made millions of dollars heading the private equity firm Bain Capital, is skilled at extracting money from supporters.

His Wednesday midday event in Charlotte drew more than 100 people who paid between $2,500 and $50,000 each, netting his campaign about $1.5 million. That night, a somewhat larger crowd at a swank club overlooking Birmingham, Ala., generated more than $2 million, campaign aides said.

A midday event Thursday in Greenville produced $1.7 million, and Romney held other fundraisers Thursday night in Boston. He has similar events scheduled this weekend and for much of next week.

The strategy is keeping him away from public events in competitive states for five straight days, barring a change in plans this weekend. He made a major speech in Ohio on Tuesday before diving into a long string of fundraisers in various states.

Some campaign strategists say the Obama and Romney camps have so much money that they can saturate the airwaves in competitive states, and further fundraising amounts to overkill.

Texas-based GOP consultant Matt Mackowiak disagrees. He said Romney himself must attend fundraisers if he expects people to fork over as much as $50,000. "You're not going to be successful with a surrogate," he said.

Soon Romney will need time to devote big amounts of time to preparing for his three debates with Obama, and final-sprint campaigning, Mackowiak said, "so they're trying to pack in the fundraising before Labor Day."

Top-tier donors get private time to chat with Romney, out of reporters' sight. Those giving less money attend larger gatherings in which Romney gives a basic speech emphasizing the importance of entrepreneurs who create jobs.

He has been greatly impressed by "the power of individuals, the power of a citizen, a person, to change things for the better," he told the Greenville luncheon group.

Romney managed to stay in the news this week by taking reporters' questions Thursday in South Carolina, where he was pressed about his personal tax returns. Like Obama, he often grants interviews, by satellite, to local TV stations in swing states.

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  • King Tut's Penis

    Seriously, we know more about a 3,300-year-old teen pharaoh mummy penis than we do about what lies carefully preserved in Romney's tax returns before 2010. That's either because we <a href="http://www.newscientist.com/blogs/culturelab/2010/06/on-the-trail-of-tutankhamens-penis.html" target="_hplink">know a fair amount about King Tut's mummified member</a> -- like the fact that it broke off and went missing for a while -- or because we know absolutely nothing about the pre-2010 presidential candidate's tax returns.

  • Coca-Cola's Secret Formula

    Despite the presence of a number of <a href="http://en.wikipedia.org/wiki/Coca-Cola_formula#Purported_secret_recipes" target="_hplink">purported recipes</a> for Coca-Cola, the company has long maintained that there is only a single copy of the actual formula, kept stashed away in a safe place. Last year, however, Coke <a href="http://www.thecoca-colacompany.com/dynamic/press_center/2011/12/coca-cola-secret-formula-moves-to-the-world-of-coca-cola.html" target="_hplink">moved its secret formula</a> to a vault housed at the World of Coca-Cola in Atlanta. Sure, it was only a token step toward disclosure -- and probably more about making money -- but at least it was something. Your move, Mr. Romney.

  • The Bermuda Triangle

    This region may be great for <a href="http://www.vanityfair.com/politics/2012/08/investigating-mitt-romney-offshore-accounts" target="_hplink">stashing tons of Romney's money</a>, but it isn't some sort of <a href="http://en.wikipedia.org/wiki/Bermuda_Triangle" target="_hplink">isosceles zone</a> of supernatural trickery. Detailed reports of notorious shipwrecks in this area have led most experts to conclude they were caused by bad weather, rogue waves or simply human error.

  • How To Speak Prairie Dog

    <a href="http://www.youtube.com/watch?v=y1kXCh496U0" target="_hplink">Those noises</a> might sound like just a bunch of annoying, high-pitched chirps, but <a href="http://news.bbc.co.uk/earth/hi/earth_news/newsid_8493000/8493089.stm" target="_hplink">Professor Con Slobodchikoff of Northern Arizona University has more discerning ears than you</a> -- and probably a cooler name, too. Slobodchikoff says the language of the prairie dog is the most complex of any animal decoded so far. The varmints (which Romney <a href="http://www.youtube.com/watch?v=w-iRlBH3G6A" target="_hplink">may or may not enjoy hunting</a>) even have different calls for different predators. According to Slobodchikoff's studies, prairie dogs can alter their pitch and frequency to specify the size and distance of whatever is approaching.

  • Donald Trump's Mystery Hair

    Trump and Romney might have a lot of things in common -- their mutual <a href="http://abcnews.go.com/blogs/politics/2011/04/since-president-obama-released-his-birth-certificate-will-donald-trump-release-his-tax-returns/" target="_hplink">fear of releasing tax returns</a> comes to mind. But when it comes to coiffure, they are worlds apart. There have long been questions about Trump's hair. Mainly, "What is that thing on Donald Trump's head?" Well, according to him, it's just hair, carefully manicured and positioned every morning so as to make sure that no mortal can ever catch a glimpse of his forehead. From what we know, there's actually only been <a href="http://www.youtube.com/watch?v=ezz1BkuE1Qg" target="_hplink">one known sighting</a> of that part of his body. Here's what Trump <a href="http://www.rollingstone.com/culture/news/donald-trump-lets-his-hair-down-20110511" target="_hplink">told <em>Rolling Stone</em></a> about his hair: <blockquote>"OK, what I do is, wash it with Head and Shoulders. I don't dry it, though. I let it dry by itself. It takes about an hour. Then I read papers and things. This morning I read in the <em>New York Post</em> ... I also watch TV. I love Fox, I like Morning Joe, I like that the Today show did a beautiful piece on me yesterday -- I mean, relatively speaking. OK, so I've done all that. I then comb my hair. Yes, I do use a comb ... Do I comb it forward? No, I don't comb it forward ... I actually don't have a bad hairline. When you think about it, it's not bad. I mean, I get a lot of credit for comb-overs. But it's not really a comb-over. It's sort of a little bit forward and back. I've combed it the same way for years. Same thing, every time."</blockquote>

  • Area 51

    Like Mitt Romney's tax returns, this Nevada military base is shrouded in a thick veil of secrecy. While there is undoubtedly a lot of stuff going on in there -- most of it likely far more interesting than Romney's tax history -- Americans aren't completely in the dark about the base. Since acknowledging the existence of the Air Force base, the government has predictably been hush-hush about projects at the facility. Historians have, however, have <a href="http://books.google.com/books/about/Shadow_Flights.html?id=cmMBAAAACAAJhttp://books.google.com/books/about/Shadow_Flights.html?id=cmMBAAAACAAJ" target="_hplink">written books</a> about Area 51's less juicy past. No aliens or UFOs, just some <a href="http://www.latimes.com/entertainment/la-mag-april052009-backstory,0,5104077.story" target="_hplink">advanced flight technology</a> and military procedures that have gone awry at times. But that doesn't rule out the possibility that there's a lot more going on there now. Alien spacecraft? Energy weapons? A time travel project? Your imagination's the limit. In a way, the government's approach to releasing information about Area 51 seems a lot like Romney's strategy for releasing his tax returns. Release a few boring details -- like your 2010 and 2011 forms -- only to keep everything else, presumably the most interesting stuff -- under wraps. When people ask what's going on back there, just tell them to pipe down and mind their own business. As with Area 51, Romney's method is proving an awful way to quiet speculation.

  • What Space Smells Like

    Do Mitt Romney's tax returns smell like "seared steak, hot metal and welding fumes"? If they did, they'd smell just like <a href="http://www.huffingtonpost.com/2012/07/22/what-does-space-smell-like_n_1691642.html" target="_hplink">space</a>, according to astronaut spacewalk veterans.

  • The God Particle

    <a href="http://www.huffingtonpost.com/2012/07/03/higgs-boson-explained-god-particle_n_1645732.html" target="_hplink">The God particle</a>. <a href="http://en.wikipedia.org/wiki/Higgs_boson" target="_hplink">The Higgs boson</a>. You say "potato," I say "potah ... Whaaa, come again?" To make a very long and nerdy story over-simplistically short, a bunch of really smart theoretical physicists have used a multi-billion dollar piece of equipment to prove the existence of the particle that gives mass to other elementary particles. They did this by blasting things at each other at near-light speed around a 17-mile tube track of death (or life?) located in a subterranean bunker in Europe. Is it possible that a mini hadron collider is listed as an expense on Romney's tax returns?

  • Why Sloths Are Bad At Balance And Stuff

    If the captains of the animal kingdom were picking species to partake in what Mitt Romney might call "sport," three-toed sloths might get picked dead-last -- unless that sport somehow hinged entirely upon being incredibly cute. Not only are these sloths lethargic, but they're clumsy, which is actually not a problem because they pretty much only come down from trees to poop. Because their slow-motion lifestyles afford them the luxury of being able to survive without a good sense of balance, the semi-circular ear canals that control their equilibrium <a href="http://www.huffingtonpost.com/2012/08/01/sloth-balance-bradypus-variegatus_n_1728811.html" target="_hplink">have never been honed by the evolutionary process</a>.

  • What Dinosaur Sex Looked Like

    So <em>that's</em> what it looked like, at least according to <a href="http://www.huffingtonpost.com/2012/07/09/dinosaur-sex_n_1659391.html" target="_hplink">Beverly Halstead, an Englishman </a>known for his candid talk about dinosaur mating before his death in 1991. Figuring out the "cloacal kiss" based on fossils from the Cretaceous Period must have been difficult. But it was still easier than guessing what Romney's tax returns might look like.

  • How To Survive The Zombie Apocalypse

    While <a href="http://www.huffingtonpost.com/2012/06/01/cdc-denies-zombies-existence_n_1562141.html" target="_hplink">they tell us</a> zombies aren't real ... <em>yet</em> ... that doesn't mean people aren't preparing like there's a brain-starved horde headed straight for their front door. Countless books, movies, TV shows, comics and websites provide entertainment and ideas about the best way to make it through Apocalypse Z without becoming a zombie. The Centers for Disease Control and Prevention has <a href="http://www.cdc.gov/phpr/zombies.htm" target="_hplink">hopped on board as a joke</a>, but the government's <a href="http://blogs.cdc.gov/publichealthmatters/2011/05/preparedness-101-zombie-apocalypse/" target="_hplink">preparedness guide</a> appears to be taking it pretty seriously. Too bad the CDC is only serving up a barebones list of recommendations. Wait, why do we care about a presidential wannabe's tax returns again? I'm going to draw up a contingency plan.

  • What Ryan Lochte's Mom Knows About His Sex Life

    Ike Lochte seems to know too much about her swimmer son's "<a href="http://www.huffingtonpost.com/2012/08/02/ike-lochte-ryans-mom-talks-one-night-stands-single-girlfriend-today-show_n_1733433.html" target="_hplink">one-night stands</a>." Way too much. Like "the opposite of how much we know about Romney's tax returns" too much.

  • Mitt Romney's Car Elevator

    Romney reportedly shelled out $55,000 to install a top-of-the-line "Phantom Park" car elevator in his California beachfront mansion, which will allow him to "<a href="http://abcnews.go.com/blogs/politics/2012/05/mitt-romney-ordered-55000-phantom-park-car-elevator-designer-says/" target="_hplink">maintain a hands-on relationship</a> with his machines," according to the maker. Sounds kinky. Kinky enough to make me want to read more tax returns. Oh Romney -- you <em>tease</em>.

  • President Obama's Annoying Stoner Habit

    Barack Obama was a cheeky kid who refused to observe proper stoner decorum, but author David Maraniss writes in Obama's biography that he pretty much got away with it. Here's <a href="http://www.huffingtonpost.com/2012/05/25/obama-pot-smoking-details_n_1545904.html" target="_hplink">a passage that describes</a> the future president's behavior while a member of the "Choom Gang" at his Hawaii high school. <blockquote>"When a joint was making the rounds, he often elbowed his way in, out of turn, shouted 'Intercepted!' and took an extra hit."</blockquote> We also know a little bit about Romney's adolescence. Primarily that he was kind of <a href="http://www.washingtonpost.com/politics/mitt-romneys-prep-school-classmates-recall-pranks-but-also-troubling-incidents/2012/05/10/gIQA3WOKFU_story.html" target="_hplink">a jerk</a>. More tax returns might be able to prove to the nation that he's changed a lot since then, though it's hard to think that he isn't scared they'd actually do the opposite.

  • Magnets

    <a href="http://knowyourmeme.com/memes/fcking-magnets-how-do-they-work" target="_hplink">Sorry juggalos</a>, we're pretty sure the scientists <a href="http://en.wikipedia.org/wiki/Magnetism" target="_hplink">are right</a> about this one. It's all about the magnetic fields.

  • Easter Island's Moai

    These monoliths are frequently touted as some of earth's greatest mysteries. That's because people are lazy. Researchers actually know a lot about these gargantuan rock statues. National Geographic did a <a href="http://video.nationalgeographic.com/video/national-geographic-channel/full-episodes/explorer/ngc-easter-island-underworld/" target="_hplink">lengthy series</a> on the studies of ancient Easter Island culture, and recently announced that it may have explained one of the biggest remaining unknowns: How the moai were transported. According to a <a href="http://news.nationalgeographic.com/news/2012/06/120622-easter-island-statues-moved-hunt-lipo-science-rocked/" target="_hplink">new theory</a>, they were carved so they could be rocked back and forth, or "walked," to their destination. It would have required a lot of man power, but no trees, which the island lacked for a number of years. At least that's what the archaeology suggests. The visual comparison to the left, however, makes a compelling argument that Romney could have more direct knowledge about the mighty moai.

  • How Alicia Silverstone Feeds Her Baby

    She "<a href="http://www.huffingtonpost.com/2012/03/29/alicia-silverstone-premastication-pre-chew-food_n_1389544.html" target="_hplink">premasticates</a>." That means she chews her food and spits it into the mouth of her son, who's named "Bear Blu," for some reason. Just like a bird. Thirty years of Romney's tax returns couldn't make you un-know that.

  • Amelia Earhart's Final Resting Place

    The answer to this one may be as boring as Mitt Romney wants you to believe his tax returns are. While it's exciting to concoct theories about Earhart being captured, executed, or actually <a href="http://tighar.org/Projects/Earhart/Archives/Books/BookReviews/earhartsurvive.html" target="_hplink">surviving to assume another identity</a> and live out her life in the great state of New Jersey, the far more likely scenario is that she perished on a remote tropical island in the southwest Pacific. Discovery <a href="http://news.discovery.com/history/amelia-earhart-resting-place.html" target="_hplink">reports</a> that researchers believe evidence found on the island of Nikumaroro suggests Earhart and her navigator, Fred Noonan, died there after an emergency landing. In 1940, a British Colonial Service found skeletal remains on the island consistent with a woman of European descent. Near those bones lay a woman's shoe, an empty bottle and a sextant box for a piece of equipment similar to the one Noonan had used. According to Discovery, they "likely eventually succumbed to any number of causes, including injury and infection, food poisoning from toxic fish, or simply dehydration," at which point their bones may have been picked clean and carried off by enormous coconut crabs.

  • John Boehner's Tan

    If you believe House Speaker John Boehner (R-Ohio), his tan is natural, thanks entirely to genetics, <a href="http://www.politicsdaily.com/2010/09/08/john-boehner-defends-his-famous-tan/" target="_hplink">lawn-mowing</a>, mountain biking and a heavy dose of golf. "I have never been in a tanning bed or used a tanning product," he <a href="http://www.huffingtonpost.com/2010/09/23/john-boehner-tanning-bed_n_736897.html" target="_hplink">said in a 2010 interview</a>. In the absence of any other evidence, we'll have to take his word for it. In this case, it doesn't bother me in the slightest.