As well as the White House, Democrats and Republicans are locked in a tight race for control of the US Senate.
Republicans hold a 53-47 majority in the upper chamber of Congress, meaning the Democrats are seeking a net gain of four seats.
Five seats, including some tight battleground contests in Georgia and North Carolina, are yet to be decided.
Democrats are also fighting to maintain their majority in the lower chamber, the House, and are ahead in the polls.
But with many votes still to be counted, the final result of both races may not be known for some time. (BBC)
