5 unforgettable moments in U.S. presidential debate history

Even before the age of social media, gaffes made by U.S. presidential candidates during the election debates had the potential to dog them for years and in some extreme cases do irreparable damage that cost them the election.

In the case of some presidential hopefuls, certain catchphrases or quips became the most memorable things about them. Who can forget, for example, Ross Perot's "Let me finish!" — variations of which he uttered repeatedly during the 1992 electoral campaign.

With the first presidential debate between White House hopefuls Hillary Clinton and Donald Trump set to air Sept. 26, we take a look back at some of the unforgettable moments in U.S. debate history.

1. John F. Kennedy vs. Richard Nixon (1960)

In the first televised presidential debate, Republican candidate Richard Nixon appeared less than camera ready next to Democratic opponent John F. Kennedy.

The evening got off to a rough start for Nixon, who was battling the flu and injured his knee on the way to the studio. In comparison to Kennedy, who was clean shaven and confidently addressed the camera directly, Nixon had a five o'clock shadow and looked pale and clammy, sweating profusely throughout the debate.

His tendency to direct responses to reporters standing off stage did not help matters.

2. Gerald Ford vs. Jimmy Carter (1976)

While attempting to make a point in the 1976 debate against Democrat Jimmy Carter, Republican candidate Gerald Ford boldly declared, "There is no Soviet domination of Eastern Europe" — insisting that countries like Poland, Romania and Yugoslavia had autonomy from the Soviet Union. 

The gaffe was ultimately dubbed, "the blooper heard 'round the world."

3. Ronald Reagan (1984)

During his second run for president, the issue of Ronald Reagan's age cropped up regularly. At 73, some wondered if he was "too old to run for president." When the question was posed during a presidential debate with Democrat opponent Walter Mondale, Reagan quipped, "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."

4. Lloyd Bentsen vs. Dan Quayle (1988)

In what has been called "the greatest political zinger of all time," vice-presidential contender Lloyd Bentsen delivered a harsh blow against his much younger opponent, Dan Quayle, whose looks elicited comparisons to John F. Kennedy.

When Quayle brought up the comparison during the debate, Bentsen quipped, "I served with Jack Kennedy. I knew Jack Kennedy. Jack Kennedy was a friend of mine. Senator, you're no Jack Kennedy."

5. George W. Bush vs. Al Gore (2000)

During his run against George W. Bush, Al Gore sighed his way through most of the third presidential debate.

However, the highlight of the evening came when the Democratic candidate left his podium and walked up to Bush while he was speaking in an attempt to intimidate the Republican candidate.

Bush simply nodded his head and said, "Hello," and continued with his statement.