This combination of file pictures shows US Republican presidential candidate Mitt Romney's wife Ann (L) speaking at the Republican National Convention (RNC) at the Tampa Bay Times Forum in Tampa, Florida, on August 28, 2012, and US First Lady Michelle Obama (R) delivering a speech at the Time Warner Cable Arena in Charlotte, North Carolina, on September 4, 2012 on the first day of the Democratic National Convention (DNC). AFP PHOTO/Jewel SAMAD / Robyn BECK

This combination of file pictures shows US President Barack Obama (L) chating with a child as he visits the Countryside barbecue restaurant lunch in Marion, North Carolina, on October 17, 2011, and US Republican presidential candidate Mitt Romney (R) talking with supporters during a campaign stop at Tom's Ice Cream Bowl in Zanesville, Ohio, on August 14, 2012. AFP Photo/ Jewel SAMAD / Saul LOEB

This combination of file pictures shows US President Barack Obama (L) removing his jacket after arriving at Tampa International Airport on September 20, 2012 in Tampa, Florida, and US Republican presidential candidate Mitt Romney (R) puting on his jacket before departing Newark airport in New Jersey for Ohio where he will address a campaign rally on September 14, 2012. AFP PHOTO/ Brendan SMIALOWSKI /Nicholas KAMM

This combination of file pictures shows US President Barack Obama (L) eating shaved ice at Tropical Sno in Denison, Iowa, August 13, 2012 during his three-day campaign bus tour through Iowa, and US Republican presidential candidate Mitt Romney (R) eating ice cream during a campaign stop at Tom's Ice Cream Bowl in Zanesville, Ohio, August 14, 2012. AFP PHOTO/ Jim WATSON / Saul LOEB

This combination of file pictures shows US President Barack Obama (L) boarding Air Force One at Andrews Air Force Base in Maryland on January 19, 2012 to leave to visit Walt Disney World Resort in Florida, US Republican presidential candidate Mitt Romney (R) disembarking from his campaign plane at St. Paul International Airport in Minneapolis, Minnesota, on August 23, 2012. AFP PHOTO/Jewel Samad

This combination of file pictures shows US President Barack Obama (L) greeting supporters after speaking during a campaign event at the Henry Maier Festival in Milwaukee, Wisconsin, September 22, 2012, and US Republican Presidential candidate Mitt Romney (R) greeting the crowd after delivering remarks at a campaign rally September 13, 2012, at Van Dyck Park, in Fairfax, Virginia. AFP PHOTO / Saul LOEB /Paul J. Richards

This combination of file pictures shows US President Barack Obama (L) arriving at the Convention Centre in Cartagena, Colombia to attend the opening of the VI Americas Summit on April 14, 2012, and US Republican presidential candidate Mitt Romney (R) waving as he arrives in Portsmouth, New Hampshire, on August 25, 2012. AFP PHOTO / ALFREDO ESTRELLA /Jewel SAMAD

This combination of file pictures shows (L) veterans at the American Legion Post 176 praying before US Republican presidential candidate Mitt Romney speaks at "Veterans for Romney" campaign event in Springfield, Virginia, on September 27, 2012, and (R) a man wearing an Obama tie at the Time Warner Cable Arena in Charlotte, North Carolina, on September 5, 2012 on the second day of the Democratic National Convention (DNC). AFP PHOTO/ Jewel SAMAD / Robyn BECK

This combination of file pictures shows US First Lady Michelle Obama (L) waving to supporters at the Time Warner Cable Arena in Charlotte, North Carolina, on September 4, 2012 on the first day of the Democratic National Convention (DNC), and US Republican presidential candidate Mitt Romney's wife Ann (R) greeting the crowd of supporters at the Tampa Bay Times Forum in Tampa, Florida, on August 28, 2012 during the Republican National Convention. AFP PHOTO Stan HONDA

This combination of file pictures shows (L) US President Barack Obama during an interview on the "Tonight Show with Jay Leno" at the NBC Studios in Burbank, California, on October 25, 2011, and (R) US Republican presidential candidate Mitt Romney speaking with Jay Leno during The Tonight Show With Jay Leno on March 27, 2012 in Burbank, California. AFP PHOTO / Jewel Samad/AFP - NBC UNIVERSAL /Paul Drinkwater

This combination of file pictures shows US President Barack Obama (L) waving as he steps off Air Force One upon arrival at King County International Airport in Seattle on September 25, 2011, and US Republican presidential candidate Mitt Romney (R) boarding his campaign plane after a campaign rally September 24, 2012 at Pueblo Memorial Airport in Pueblo, Colorado September 24, 2012. AFP PHOTO/Mandel NGAN

This combination of file pictures shows US President Barack Obama (L) speaking during a campaign event at Prime Osborn Convention Center July 19, 2012 in Jacksonville, Florida, and US Republican presidential hopeful Mitt Romney (R) addressing the Family Research Council's Values Voter Summit in Washington on October 8, 2011. AFP PHOTO/Mandel NGAN /Nicholas KAMM

This combination of file pictures shows US President Barack Obama (L) greeting supporters after speaking at a campaign event at Eden Park September 17, 2012 in Cincinnati, Ohio, and US Republican presidential candidate Mitt Romney (R) greeting supporters during a campaign event at the Ross County Court House in Chillicothe, Ohio, August 14, 2012. AFP PHOTO/Brendan SMIALOWSKI / Saul LOEB

This combination of file pictures shows US Republican presidential candidate Mitt Romney (L) boarding his campaign plane at Tampa International Airport in Tampa, Florida, on August 29, 2012 en route to Indianapolis, Indiana, and US President Barack Obama (R) walking to Air Force One at Andrews Air Force Base September 17, 2012 in Maryland. AFP PHOTO/Jewel Samad /Brendan SMIALOWSKI

This combination of file pictures shows US Republican presidential candidate Mitt Romney (L) speaking during a campaign rally at Flagler College in St. Augustine, Florida, August 13, 2012, and US President Barack Obama (R) pausing while speaking during a campaign event in Lions Park a September 13, 2012 in Golden, Colorado. AFP PHOTO / Saul LOEB /Brendan SMIALOWSKI