5 unforgettable moments in U.S. presidential debate history

Even before the age of social media, gaffes made by U.S. presidentialcandidates during the election debateshad the potential to dog them for years and in some extreme cases doirreparable damage that costthem the election.

In the case of some presidential hopefuls, certaincatchphrasesor quips becamethe most memorable things about them.Who can forget, for example,RossPerot'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 alook 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 startfor 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 directresponses to reporters standing off stage did not help matters.

2. GeraldFord 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 thatcountries likePoland, 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 posedduring a presidentialdebate 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'syouth and inexperience."

4. LloydBentsenvs. DanQuayle(1988)

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

WhenQuaylebrought up the comparison during the debate,Bentsenquipped, "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 thirdpresidential debate.

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

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