In 1992, President George H.W. Bush made headlines for checking his watch as an audience member asked him a question during a debate with Bill Clinton. Eight years later in 2000, Al Gore's audible sighing during a debate with George W. Bush raised eyebrows, prompting the then-vice president to promise in an interview to "sigh a little bit less" in upcoming showdowns.
In the 2016 election cycle, GOP frontrunner Donald Trump's odd facial expressions and movements have amused debate viewers, for sure. But unlike Bush and Gore, who were heavily criticized for their relatively subtle non-verbal cues, Trump's over-the-top gestures haven't cost him any points in the polls. Why?
"Donald Trump gets different rules," said Benjamin Bates, associate professor of communication studies at Ohio University and expert in election advertising and messaging, in a phone interview.
Trump's willingness to use aggressive, nonverbal forms of communication appears to be more accepted this election cycle than perhaps it would have been in previous years, Bates explained. The pugnacious billionaire's unconventional ways of getting his point across -- even when it's not his turn to speak -- isn't being held against him by voters.
"It's been a real conundrum from an analytical point of view," said Erik Bucy, a professor of strategic communication at Texas Tech University and expert in nonverbal communication in political news. "He does things that are so outrageous with his face that any conventional politician would have been penalized for it. He's just channeling outrage and voter anger to the extent that he can use these expressions to reinforce voter animosity towards whatever issue or person or event he's mocking."
Chris Christie, whose loud, confrontational, tell-it-like-it-is persona largely mirrors Trump's (some have even argued the New Jersey governor actually nailed the brand down first), has been afforded no such luxury. His New Jersey bellicosity can register poorly with voters, because unlike Trump, the entertainer, Christie, the governor, faces different expectations.
"Because he's a governor, he's supposed to be better behaved in the debates," said Bates.
The same goes for former Florida Governor Jeb Bush and current Ohio Governor John Kasich, both of whom have struggled in debates and in the polls.
Bucy contrasted Kasich's appeal with that Senator Marco Rubio, who, while significantly less politically experienced, has a very put-together stage presence and appealing aura.
"He does seem very polished," Bucy said. "The question is, can his rhetoric and messaging rise to the level of his visual presentation? That's the challenge."
Each candidate faces a unique task in calibrating his or her verbal and non-verbal message, and neither part can be discounted. In fact, it may be what they don't say that matters more.
"I would say if there is a direct competition, it would be better to be more effective non-verbally than verbally," Bucy said.
Perhaps that's why Carly Fiorina worries she doesn't smile enough.
Some candidates tend to show small amounts of stress when on the debate stage with small, non-verbal ticks. This "tension leakage," Bucy explained, causes candidates to be evaluated worse by the audience. And even though they may otherwise appear put together, these minute signs of nervousness are perceived by viewers and can undermine the message.
President Obama was widely regarded as the loser of his first presidential debate against Romney in 2012 after demonstrating tension leakage, including blinking often and avoiding eye contact with the camera.
What ultimately matters, however, is not necessarily what the candidates do or the norms by which they abide, but instead how they are perceived by the audience, within the confines of the debate and beyond.
In the first presidential debate of this election cycle, Ben Carson's way of communicating was largely well received by viewers as measured, calm and deliberate. But as election season has dragged on and the retired neurosurgeon has declined in the polls, his manner has garnered more criticism, with some even joking that during the events he appears to have fallen asleep.
"Nothing changed about the way Ben Carson communicated, something changed in the way the audience perceived his slow, careful speech," Bates said.
Perception is what has allowed Trump to defy the odds. His supporters have proven time and again that they'll back him no matter what he does, and perhaps we all give Trump, a reality star, a little more leeway than we do the rest.
"If [the audience] is expecting Donald Trump from 'The Apprentice,' or they're expecting Ben Carson, neurosurgeon, scientific genius, they're going to have a different set of standards for them than for your usual politicians," said Bates.