In pictures: Barack Obama triumphs in 2012 US election

U.S. President Barack Obama smiles during his election night victory speech in Chicago, November 7, 2012. REUTERS/Kevin Lamarque (UNITED STATES - Tags: POLITICS ELECTIONS USA PRESIDENTIAL ELECTION) *** Local Caption *** CHI524_USA-CAMPAIGN_1107_11.JPG

Ajay Narayan cheers as the race is called for US President Barack Obama by a television network during the Nevada State Democrats' election night party at the Mandalay Bay Resort in Las Vegas. Sam Morris / Reuters

Supporters of Republican challenger Mitt Romney react as they watch voting returns at the election night rally for Romney in Boston, Massachusetts. Shannon Stapleton / Reuters

Mitt Romney arrives on stage to concede the election to President Barack Obama. Don Emmert / AFP

Supporters of US President Barack Obama cheer as they wait for him to appear on stage for his victory speech at McCormick Place in Chicago, Illinois. Spencer Platt / Reuters

A young Republican supporter shows her disappointment as the results come in during Republican presidential candidate Romney's election night rally. David Goldman / AP

Republican presidential nominee Mitt Romney, left, and his vice presidential nominee Paul Ryan hug as their wives Ann Romney and Janna Ryan, right, do the same after Romney delivered his concession speech. Mike Segar / Reuters

The re-elected Barack Obama and his vice president Joe Biden, left, embrace after President Obama gave his acceptance speech. Adrees Latif / Reuters

Despair among Republican supporters after only the second time in several decades that a Democrat has won a second term in the White House. Emmanuel Dunand / AFP

Tears of joy as President Obama delivered his victory speech. Matt Rourke AP Photo

People celebrate in Times Square, New York, after it was announced that President Obama has been re-elected. Mehdi Taamallah / AFP

Barack Obama is met on stage by first lady Michelle Obama and daughters Sasha and Malia after his victory speech. Spencer Platt / AFP