Body language is a critical part of how candidates are perceived by voters, and many candidates invest hours honing how they come across to millions watching on television.
So ABC News went to three body language experts for their opinions on how each candidate was portraying himself or herself during the debate.
Here’s what they told us:
Joe Navarro, former FBI agent: Notice Trump’s emphasis and use of a precision grip as he says that he doesn't forgive people who let him down. We usually only use that precision grip -- index finger to thumb -- when we have certainty about one topic or sentiment. Also see that Trump is the only one that touches the microphone, which is a territorial display. It says that everything in front of me is mine -- not just the podium, but what’s on the podium.
Janine Driver, body language instructor: Trump once again "keeps it real." From acting like a little kid mocking Kasich, to "like-what-I'm-saying-right-now" a-okay steeples, to more aggressive palm-down gestures, pointing and chopping, all his moves are all integrated, which means Trump is being authentic. He’s saying we don't need to second-guess or question if his opinions are genuine.
John Neffinger, communications coach: Trump brought his signature style, forceful but under control. But he's not having as much fun as he was in the first debate, the novelty has worn off, and the polls may have rattled him. His gestures are smooth when he's confident and jerky when he's agitated, and tonight they were more jerky. He's also overusing a particularly funny clown face where he pinches the sides of his mouth. Again, tension.
Navarro: We tend to gravitate to those who appear in control, measured, deliberate, even-tempered. Dr. Carson is the only speaker to steeple his fingers -- touching fingertip to fingertip. It is one of the few signs that we humans have of confidence. Is there a downside to this demeanor? Yes. Someone who takes too long to answer, is too deliberative or seems incapable of quickly answering will in a debate format not come across well.
Driver: Carson’s body movements tend to be more free-flowing then all of the other candidates. For instance, we see non-verbals like a decrease in pressure, which indicates a softer approach to persisting against difficult odds -- ultimately a less aggressive way to being determined. Dr. Carson also often kept his hands in an almost-humble-like pose where he puts his right hand on top of his left hand like he's in church.
Neffinger: Ben Carson's soft vocal tone, slow pacing and gentle motion suggest not only that he is thoughtful, but that he is calm. That calm confidence has a deep, reassuring appeal. He is not the only person on stage who has not been a professional politician, but he's the only one who seems like a regular person, someone who might be a neighbor.
Navarro: He didn’t do much nonverbally, except we did not see as much smiling toward Donald Trump as before in other debates. It is through nonverbals and passion that we demonstrate how much we care: it is the exclamation point. Jeb Bush demonstrated little passion for his arguments or beliefs unlike the other candidates, especially those low on the scale. He failed to convince through his nonverbals.
Driver: I feel that Jeb Bush came out looking like he just didn't want to be there. When the camera scanned to him at the beginning of the debates, Bush's facial expression appeared nervous. Later, Bush even shook his head "no" when he said that his plan gives the middle-class the biggest break.
Neffinger: Jeb can look great in well-made ads, and he has the money to make them. But he does not appear confident: stooping, wincing and shrugging.
Navarro: She did continue to impress nonverbally in several ways. She has an emphasis that is consistent with her rhetoric in the form of hand, arm and finger gestures. And we also must consider the speed of her responses, which were immediate -- indicative of preparation, but also a facile mind.
Driver: Fiorina smiled more and her body movements were more integrated, which sends a message that she seemed to be more in the moment. However, there were a couple dips in her likability or openness, like when her lip disappeared when she was asked should she really be bragging that Perkins is plugging her. When we don't like what we see or hear, our lips disappear.
Neffinger: Carly projected confidence but not aggression, did not get testy and smiled once or twice. She turned several answers into inspiring red-meat speeches. But she's basically projecting all strength and control, very little warmth or hope.
ABC News: Marco Rubio is often seen as an establishment dark horse in the GOP nomination race. What makes Rubio’s debate performances so effective?
Navarro: Over and over, Rubio excels with the nonverbals of speed, how quickly he answers and the lack of speech errors, like “uhh” and “umm.” Rubio is not just articulate: he is passionate. You can see in his gestures and his facial expressions that he is adamant and with confidence. Notice the speed at which Rubio speaks: speed of speech is a nonverbal, it entices. He also uses facial displays that don’t betray his dislike of questions, unlike Cruz or Trump.
Driver: Marco Rubio’s not overly stiff posture sent the message that his confidence-level was up high. Not surprisingly, the time we saw Rubio hold back was when he was first asked about should he retire from his current job. He held onto the podium for dear life then became more animated when mentioning other politicians who have done the same thing.
Neffinger: Rubio's answers were like miniature speeches: his intonation is grandiloquent, and his gestures are also crisp and poised. I think it's unlikely he said much tonight that he hadn't practiced extensively. But his facial expression often seems flat or uneasy, and he doesn't connect emotionally.
ABC News: Ted Cruz lashed out against the moderators during the debate, saying that the questions asked of the candidates were more like attacks. What do you make of that outburst?
Navarro: Cruz was focused on one message and he kept repeating himself. That is not good. People see that as being out of control - especially when something is emotionally repeated multiple times. It may appeal to supporters of Cruz, but it turns many more off.
Driver: Interestingly, when Cruz attacks the media, his head is slightly tilted to his left, which increases likability. So although his hand gestures and pitch and tone of voice are aggressive, that slight head tilt may make him not look like a bully. Also, when he got an applause-break for his comments, his bottom lip pursed in a micro-expression of sadness. Again, this will be likely seen by many as humbling instead of arrogant.
Neffinger: Cruz opened the debate by poking fun at himself about how laid-back he was(n't), a clear and successful effort to soften his image. With his mostly pre-planned takedown of the media later, he took that effort a memorable step further, calling out the moderators on behalf of all Republicans listening. But instead of righteously pounding the podium, he adopted a comfortably world-weary tone, as if to say "come on now, guys," and gently ribbed the moderators of the Democratic debate for pitching softballs. This warm tone nicely balanced the strength move of hijacking the question to criticize the questioner.
ABC News: Anything else stand out to you?
Navarro: It seemed this time they were more passionate and gesturing more, certainly on the part of Kasich, Cruz, Christie and Huckabee -- as expected, because they have to be more dramatic. And the entry seemed rather muted to me. There wasn’t a lot of pointing at audience members like we have seen before.
Driver: Both Trump and Kasich jet their right shoulders out towards the moderators when they don't like what any of the other candidates or the moderators say about them. This has to do with the way our brains are wired to process emotions: we literally angle our left shoulder to open up conversation and our right shoulder when we get defensive.
Neffinger: Overall, tonight's debate was a pretty good showing for the Republican Party. Jeb Bush looked awkward and Rand Paul looked unimpressed -- "low energy" as Trump might say -- but everyone else looked at least professional, if not quite presidential.