The presidential debates between Hillary Clinton and Donald Trump are expected to draw a record number of television viewers.
But pre-election head-to-heads have been shaping and influencing the course of the election for more than 50 years.
In the first-ever televised debate, Senator Jack Kennedy found himself taking on then-Vice President Richard Nixon.
Mr Nixon refused to have makeup applied for the television cameras, making him appear sweaty and uneasy.
Those listening on radio thought Mr Nixon had won, but TV viewers were certain Mr Kennedy was better.
In 1984, many saw 73-year-old Ronald Reagan as too old to be re-elected Commander in Chief.
But when pushed on the matter, the Republican nominee cunningly turned it against his opponent.
"I will not make age an issue of this campaign," Mr Reagan said. "I am not going to exploit for political purposes my opponent's youth and inexperience."
The 2000 election was one of the closest in history - Vice President Al Gore wasn't going to be upstaged by Texas Governor George W Bush.
At one point in their debates, Mr Gore appeared to be intimidating Mr Bush by invading his personal space - a move that surely backfired.
In 2012, Mitt Romney provided keyboard warriors with mountains of ammunition when he took on Barack Obama and bragged about his pay equity record.
He was trying to explain how he hired female employees, when he said: "I went to a number of women's groups... and they brought us whole binders full of women."
Within minutes the phrase "binders full of women" became infamous online, with countless memes cropping up almost instantly.
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