The televised presidential debates have played a key role in many of the US election campaigns since the 1960 Kennedy-Nixon contest. Here are some of the dramatic moments which changed the course of election history.
Lloyd Bentsen puts Dan Quayle in his place during their 1988 debate.
One of the few memorable vice-presidential debates took place in October 1988 between Democratic Senator Lloyd Bentsen and Republican nominee Dan Quayle.
Senator Bentsen attacked Mr Quayle for invoking the memory of President John F Kennedy.
But despite his success in the debate, it had little effect on the outcome of the election, which was easily won by Republican Vice-President George HW Bush.
Al Gore shakes his head as George W Bush has his say on education
Al Gore took a dismissive stance during the first of his three presidential debates with George W Bush in 2000.
Mr Gore was seen shaking his head and rolling his eyes during their clash on 3 October - a move that did not go down well with some of those watching.
The 2000 election turned out to be one of the closest in history, with victory declared only after the Supreme Court ruled on the contested Florida vote.
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