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.
KENNEDY-NIXON DEBATE - SEPTEMBER 1960
Kennedy looks calm while Nixon appears flustered
The first televised presidential debate took place on 26 September 1960.
Vice-President Richard Nixon was widely expected to win the debate against the more inexperienced Senator John F Kennedy.
But the cameras favoured Mr Kennedy, who looked calm and composed throughout, while Mr Nixon appeared unshaven and flustered.
FORD-CARTER DEBATE OCTOBER 1976
President Ford raised eyebrows with his comments on Soviet domination
President Gerald Ford raised eyebrows in his clash with Jimmy Carter when he insisted there was "no Soviet domination of Eastern Europe".
His gaffe came on 6 October, in the second of three debates between the contenders in the 1976 presidential race.
Mr Ford lost the subsequent election. He had assumed the presidency in 1974 when Richard Nixon resigned after the Watergate scandal.
CARTER-REAGAN DEBATE OCTOBER 1980
Reagan challenges voters to reflect of Carter's time in office
Ronald Reagan challenged voters to reflect on President Jimmy Carter's time in office as time was called on their 1980 debate.
The two men went head-to-head on 28 October, in the only debate of the election race to feature them both.
With inflation soaring and huge lines at petrol stations as a result of the energy crisis, Mr Reagan went on to defeat the sitting president.
REAGAN-MONDALE DEBATE OCTOBER 1984
President Reagan shows age has not dulled his sense of humour
President Ronald Reagan showed age had not dulled his sense of humour with a well-timed quip as he clashed with Walter Mondale.
His remarks came on 21 October, in the second of two presidential debates during the 1984 election race.
President Reagan went on to win re-election in a landslide victory.
DUKAKIS-BUSH DEBATE OCTOBER 1988
Michael Dukakis stands firm on the issue of capital punishment
Michael Dukakis was put on the spot with a question about capital punishment during one of his debates with Vice-President George HW Bush.
The incident came on 13 October, in the second of two presidential debates during the 1988 election, and helped Mr Bush to victory.
BENTSEN-QUAYLE DEBATE OCTOBER 1988
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.
BUSH-GORE DEBATE OCTOBER 2000
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.