During the Second 2016Presidential Debate (in the video above, from 57:08 - 57:12), Donald Trump can be seen displaying in a very particular Body Language cluster-configuration.
Mr. Trump, with his feet in a wide stance, leans laterally left with his weight shifted, his left arm wide with his left hand is on the back of his chair, his right thumb is hooked inside his belt (or pants) with the remainder of his hand hanging loosely over his central, lower abdomen. Moreover during 57:10 Trump pulls up on his belt-pants in this central region - in a False Adjustment maneuver. He's also "Whole Body Pointing" toward Hillary Clinton.
Mr. Trump did something similar (but even more dramatic) last November when refuting a story of Ben Carson's (See: Nonverbal Communication Analysis No. 3375: Donald Trump Questions Ben Carson's Stabbing Story).
In body language parlance, this is an example of a "MAP Surrogate" (Manipulator, Adaptor, Pacifier) - as well as a variation of a Partial Emblematic Slip. This dramatic act is very out of context for anyone on stage (other than during a true drama/play) and certainly during any kind of a political debate. This a Hyper-Alpha Sexual Display with Donald Trump attempting to project dominance and virility.
See also:
Nonverbal Communication Analysis No. 3723: The 2nd Presidential Debate - Donald Trump v. Hillary Clinton
Nonverbal Communication Analysis No. 3721: The 2nd Presidential Debate - Donald Trump v. Hillary Clinton - The Handshake That Wasn't
Nonverbal Communication Analysis No. 3719: Donald Trump's "Apology" - Crisis Management, Body Language and Emotional Intelligence
Nonverbal Communication Analysis No. 3716: Fatherhood, Body Language, Emotional Intelligence and Ashton Kutcher's Pants
Nonverbal Communication Analysis No. 3711: Vin Scully calls Kirk Gibson's legendary walk-off homer during Game 1 of the 1988 World Series
Nonverbal Communication Analysis No. 3706: Hillary Clinton v. Donald Trump Presidential Debates - Part II
Nonverbal Communication Analysis No. 3704: Hillary Clinton, Likability and Presidential Debates
Nonverbal Communication Analysis No. 3611: Salma Hayek, Danny Trejo and a Tattoo
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