A record number of Americans are expected to be glued to their TV sets when Mrs Hillary Clinton and Mr Donald Trump step on the debate stage together for the first time next week on Monday (Sep 26, US time). Pressure is on both presidential candidates as the high-stakes debate could be potential game-changer, especially in an extremely tight race.
Here is a look at five moments that have made an impact in the history of US political debates:
1. FORD'S SOVIET BLUNDER
In a moment that has come to embody the ultimate presidential debate gaffe, President Gerald Ford claimed in a 1976 debate against challenger Jimmy Carter that there was "no Soviet domination of Eastern Europe and there never will be under a Ford administration", despite widespread agreement to the contrary.
The statement was so shocking the journalist who asked the question did a double take and asked if Mr Ford meant what he said. Mr Ford's claim made him sound uninformed about global geo-politics. Time Magazine called it the "blooper heard round the world".
2. REAGAN'S AGE, NO ISSUE
In 1984, some Democrats began to question if President Ronald Reagan, then 73, had become too old to continue as president effectively. When this came up in a debate, he delivered a deftly crafted line that put the issue to bed and even had his rival Walter Mondale laughing.
"I will not make age an issue of this campaign. I am not going to exploit, for political purposes, my opponent's youth and inexperience," he said in what has become known as one of the best lines ever delivered in a presidential debate.
3. GORE'S SIGH
Sometimes, a candidate's debate performance can be undone by what is unsaid. In 2000, Mr Al Gore, then the Vice-President, learnt that the hard way when he made a loud sigh while then Texas Governor George W. Bush was talking. The sigh made Mr Gore look condescending and stand-offish. Pundits said the sigh mattered almost as much as any response he gave.
4. BUSH'S TIME CHECK
If you blink you may miss it but the cameras did not - and so the moment when President George H.W. Bush checked his watch as a voter asked him a question was replayed time and again in the election of 1992. It made the incumbent look unengaged - in contrast to upstart Bill Clinton, who would get up from his chair and walk right up and listen intently to whoever was asking a question.
5. PERRY'S 'OOPS' MOMENT
This one took place at a primary debate rather than a presidential one, but is notable for being perhaps the clearest point at which a campaign truly went off the rails at a debate. In 2012, then Texas Governor Rick Perry found himself in a bind when he could not recall the three government agencies he wanted to shut down. He stumbled awkwardly for what felt like an eternity as other candidates could be heard chuckling, before he ended by saying " oops".