The footage shows a white man in a cowboy hat walk down the row to the aisle where protesters are leaving and sucker-punch an African-American man, later identified as Rakeem Jones.
WRAL reports that the suspect, John McGraw, 78, was charged with assault and battery on Thursday.
Moments before the attack, the protester appeared to wave a middle finger at the crowd on his way out. Men in uniforms that read “Sheriff’s Office ” were leading the protesters away.
Jones accused Cumberland County officers of failing to protect him.
“The police jumped on me like I was the one swinging," he told The Washington Post.
“My eye still hurts. It’s just shocking."
Inside Edition tracked down McGraw after the rally and asked him if he liked the rally. “You bet I liked it. Knocking the hell out of that big mouth," McGraw said.
Asked why he punched the protester, McGraw told Inside Edition, "Number one, we don’t know if he’s ISIS."
"We don’t know who he is, but we know he’s not acting like an American," McGraw went on. "The next time we see him, we might have to kill him."
An official from the Cumberland County Sheriff’s Office defended the deputies' actions at the rally on Wednesday.
"Our mission was to make sure all the 14,000 people stay safe, to separate protesters from supporters and to exit them as quickly as possible. What we did was to de-escalate the situation," Sgt. Sean Swain told The Huffington Post.
Swain also cautioned not to take a "10-second video out of context," referring to a moment where Jones is lying on the ground with deputies surrounding him, adding that "you don't know whether he fell or whether he was taken to the ground."
"When we look at all the video, we'll make final determination what took place," he said.
The sheriff's office has denied its officers detained the protester.
Democratic presidential candidate Hillary Clinton said she was "appalled" by the incident.
“Count me among those who are truly distraught and even appalled by a lot of what I see going on, what I hear being said," Clinton said in a new interview with MSNBC's Rachel Maddow, a segment of which was previewed Thursday on the network. "You don't make America great by, you know, dumping on everything that made America great, like freedom of speech and assembly and, you know, the right of people to protest."
Sen. Bernie Sanders (I-Vt.) called the violence an "ugly incident" that no one should face at a political rally. "Mr. Trump should take responsibility for addressing his supporters' violent actions," Sanders said in a statement.
Igor Bobic contributed reporting.
This article has been updated with comment from a sheriff's spokesman, Hillary Clinton and Bernie Sanders, as well as information about the suspect.