US President Barack Obama (R) embraces former President Bill Clinton onstage after Clinton nominated Obama for re-election during the second session of the Democratic National Convention in Charlotte, North Carolina, September 5, 2012. [Photo/Agencies]

US Vice-President Joe Biden (L) and first lady Michelle Obama (R) applaud as they watch from the first lady's box during the second session of the Democratic National Convention in Charlotte, North Carolina, September 5, 2012. [Photo/Agencies]