Barack Obama has won re-election to a second term as president, beating back a fierce challenge from Republican Mitt Romney.

Obama prevailed despite a weak economy and high unemployment.

A subdued Romney conceded to his supporters in Boston. He said he "left everything on the field.'' Romney offered thanks to running mate Paul Ryan, who he called the best choice he ever made beside his wife Ann.

Romney asked for unity. He said the nation is at a critical point and can't risk "partisan bickering and political posturing.'' He urged supporters and Republicans to reach across the aisle.

The former Massachusetts governor, who lost nearly all the battleground states, called on all Americans to work to rebuild the nation.

Romney called on job creators to invest and to hire workers. He said Democrats should put the "people above politics.''

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