Candidates often spend days on debate preparations trying to rehearse their talking points, master key topics and anticipate any scenario that might arise.

But often it's the impromptu clangers that become the defining moments of the debate –and could even make or break a campaign.

Here are a few memorable quips from over the years.

1980: “There you go again.”

Republican challenger Ronald Reagan's brusque quip to Democratic President Jimmy Carter after Carter accused the former California governor of starting his political career by campaigning against Medicare. 

1980: "Ask yourself, 'Are you better off now than you were four years ago?' "

Reagan asked this question to voters about Carter's administration during his debate with the 39th president.

Variations of that quote have been used by other presidential candidates since, with a recording of Reagan's comments even being used against President Donald Trump by Democratic groups this year.

1984: “I will not make age an issue in this campaign. I am not going to exploit for political purpose my opponent’s youth and inexperience.”

Reagan, then running for re-election, humorously turned the concerns that he was getting too old or senile for the job back on Democratic challenger Walter Mondale.

1988: "I served with Jack Kennedy. I knew Jack Kennedy. Jack Kennedy was a friend of mine. Senator, you're no Jack Kennedy."

Democratic vice-presidential nominee Lloyd Bentsen dismissed GOP opponent Dan Quayle's assertion that his political experience in Congress was comparable to John F. Kennedy's.

2008: “You know who voted for it? You might never know. That one!”

Senator John McCain pointing to then-Senator Barack Obama while referring to him as "that one" became a viral moment online.

McCain was talking about an energy bill that he said was "loaded down with goodies, billions for the oil companies."

McCain noted that Obama voted for the bill while he voted against it.

2012: “The 1980s are calling to ask for their foreign policy back.”

Democratic President Barack Obama's poked at Mitt Romney after the GOP challenger said Russia was the biggest geopolitical threat facing the US, not Al Qaeda, as Obama had said.

2012: "We took a concerted effort to go out and find women who had backgrounds that could be qualified to become members of our Cabinet. I went to a number of women's groups and said, 'Can you help us find folks,' and they brought us whole binders full of women."

Romney's remarks were made at the second presidential debate against Obama. Romney's line, "binders full of women," went viral online and became a meme. 

2016: “Such a nasty woman.”

Then-Republican nominee Trump described Hillary Clinton, the Democratic nominee, as such during the third presidential debate in 2016.

The phrase, "nasty woman," ended up becoming a viral meme and launched a movement of Democratic women to vote across the nation.