Texas Governor Rick Perry's inability to remember the third agency he would cut as president had many predicting the untimely end of his campaign for president.
Perry addressed his mental lapse before reporters after the debate, admitting, "Yeah I stepped in it man. Yeah it was embarrassing. Of course it was."
During a GOP primary debate in late 2011, Romney sought to put an end to then-presidential candidate Rick Perry's insistance that Romneycare was the basis of President Barack Obama's health care reform law.
Perry launched in with an attack that he'd repeated before:
"I'm just saying, you're for individual mandates, my friend," Perry said.
"You've raised that before, Rick, and you're simply wrong," Romney responded, extending his hand toward Perry. "Rick, I'll tell you what: 10,000 bucks? $10,000 bet?"
Perry declined, nothing that he wasn't a betting man, leaving Romney to quote a chapter from his book that he cited as proof he had never intended for his health care plan to be used as a national model.
At a GOP primary debate in October of 2011, Michele Bachmann (R-Minn.) criticized Obama's foreign policy decisions.
"Now with the president, he put us in Libya," she said. "He is now putting us in Africa. We already were stretched too thin, and he put our special operations forces in Africa."
Libya is, in fact, a country in Africa.
During a 2010 gubernatorial debate, Arizona Governor Jan Brewer struggled to name any of her accomplishments while introducing herself. "We have ... done so much ... We have um, did what was right for Arizona," she squeezed out after a long silent pause.
Christine O'Donnell was unable to name a single recent Supreme Court decision she disagreed with, when asked by moderator Nancy Karibjanian during a 2010 Delaware Senate debate. The dialogue:
KARIBJANIAN: What opinions, of late, that have come from our high court, do you most object to?
O'DONNELL: Oh, gosh. Um, give me a specific one. I'm sorry.
KARIBJANIAN: Actually, I can't, because I need you to tell me which ones you object to.
O'DONNELL: Um, I'm very sorry, right off the top of my head, I know that there are a lot, but I'll put it up on my website, I promise you.
When Sarah Palin and Joe Biden shook hands at the start of a 2008 vice presidential debate, Palin asked then then-Senator "Hey, Can I call you Joe?"
"You can call me Joe," Biden replied.
Palin evidently kept confusing then-Senator Joe Biden's last name with President Barack Obama's, referring to the VP candidate repeatedly as "O'Biden" in debate prep. Her staffers suggested she call him by his first name.
Hilary Clinton's attempt at a jab toward President Barack Obama got her booed by the audience during a 2008 presidential debate.
Clinton accused Obama of plagiarism in his popular speeches, saying "Lifting whole passages from someone else's speeches is not change you can believe in, it's change you can Xerox."
During a Democratic presidential primary debate in early 2008, then-candidate Hillary Clinton was being pressed on surveys that suggested New Hampshire voters appreciated her resume, but found then-Sen. Barack Obama (D-Ill.) more likable.
Clinton appeared to feign insult, drawing sympathetic applause and smiles from the crowd.
"Well, that hurts my feelings," she said. "But I'll try to go on.
"He's very likable," Clinton continued of Obama. "I agree with that. I don't think I'm that bad."
Obama took a brief break from scribbling notes to weigh in.
"You're likable enough, Hillary," Obama said tersely, not making eye contact with Clinton. He then returned to his notepad.
A 2000 presidential debate seriously hurt Al Gore's campaign when the cutaway shots caught him rolling his eyes and sighing audibly during George W. Bush's answers.
Critics say behavior made Gore look elitist and unlikable in contrast with Bush's relaxed and folksy demeanor.
Jon Stewart mocks Gore's sighs in The Daily Show clip above.
Ross Perot may go down in history for his repeated interruptions of "let me finish" during a 1992 presidential debate. The behavior became fodder for SNL comedian Dana Carvey's Perot impression.
George H. W. Bush was caught glancing at his watch during a 1992 presidential debate with Bill Clinton and Ross Perot. The now-famous move damaged Bush's campaign, making him look bored and impatient, reports say.
Bush snuck at peek at his watch again during his daughter-in-law Laura Bush's speech at the Republican convention in 2008.
When Independent Presidential candidate Ross Perot picked Vietnam War hero Admiral James Stockdale for his VP nominee, it created a rare three-person Vice Presidential debate in 1992.
Stockdale was not a politician and not very well known. Attempting to introduce itself and poke some fun at this, he chose as his opening statement: "Who am I? Why am I here?"
Stockdale later said he hoped to follow up the remarks with an explanation of his life, but never got to that point. Instead, the line left viewers wondering the same thing.
When the moderator of a 1988 presidential debate asked Governor Michael Dukakis if he would support the death penalty if his wife, Kitty Dukakis, was raped and murdered, Dukakis dispassionately responded, "No, I don't, Bernard, and I think you know that I've opposed the death penalty during all of my life." He then continued to talk about his stance.
Some believe the lack of emotion or passion for the hypothetical situation cost Dukakis the election.
In the 1988 Vice Presidential debate between Democratic VP candidate Senator Lloyd Bentsen and Republican VP candidate Senator Dan Quayle, Quayle was asked if his qualifications were sufficient to inherit the presidency, should it come to that.
Quayle responded by comparing his experience level Jack Kennedy's experience level when he sought the presidency.
The comparison prompted Bensten to say: "Senator, I served with Jack Kennedy. I knew Jack Kennedy. Jack Kennedy was a friend of mine. Senator, you're no Jack Kennedy."
Quayle responded, "That was really uncalled for Senator."
In the 1976 presidential debate between Jimmy Carter and Gerald Ford, Ford famously stated "There is no Soviet domination of Eastern Europe."
The remark came in response to a question about U.S. relations with the Soviet Union, a major concern in the Cold War era, and didn't sit well with an increasingly anti-Soviet public.
Ford refused to back down from the claim even after the somewhat baffled debate moderator responded, "I'm sorry, what? ... Did I understand you to say, sir, that the Russians are not using Eastern Europe as their own sphere of influence in occupying most of the countries there and making sure with their troops that it's a communist zone?"
The 1960 presidential debate between John F. Kennedy and Richard Nixon was the first nationally televised debate in the U.S. and is thought to have changed politics forever.
The debate was historically declared a win for Kennedy by those who watched it on TV, and a win for Nixon for those who listened to it on the radio. Though the candidates were both strong on the issues, the visibly sweating Nixon looked sickly and pale compared to the young and fit Kennedy.