Last night violence erupted between Trump supporters and anti-Trump protestors at an event in Chicago. Trump subsequently cancelled the event. Earlier today in Vandalia, Ohio, Donald Trump was rapidly surrounded by his security/Secret Service agents as a man tried to rush the stage.
In this moment (0:33) just before his security personnel had stopped the man, Trump turns toward the noise. This "turning towards a unexpected noise" is a component of the startle reflex - however the following described facial expression is not.
Although the resolution is low in this motion-captured, magnified photo, it's still easy to see Trump's left eye is opened significantly wider than baseline. The corner of his mouth is also pulled laterally and downward. Together these eyes of fear and mouth of fear make up a very recognizable body language cluster. Because it lasted only for a fraction of a second, this nonverbal display would also be an example of a microexpression. This behavior is normal for context.
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