A Donald Trump supporter at a North Carolina rally for the Republican frontrunner was videotaped by several witnesses punching a black protester in the face, then later boasted on national TV: "Next time we may have to kill him."

John Franklin McGraw, 78, sporting a pony tail and cowboy hat, was later arrested and charged with assault and disorderly conduct.

McGraw, of Linden, North Carolina, appears on video from different angles apparently both punching Rakeem Jones, 26, then knocking him in the face with his elbow. He then appears to return smiling, to his seat.

"You bet I liked ... knocking the hell out of that big mouth," McGraw told Inside Edition when interviewed by a reporter as he exited the stadium after the rally. Asked why he threw the punch, McGraw, said: "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.

"He deserved it. The next time we see him, we might have to kill him. We don't know who he is. He might be with a terrorist."

The attack occurred as police were escorting Jones and a handful of other protesters from the stands at Lafayette stadium during a Trump rally. After Jones was struck and was staggering, police appeared to pounce on him, pushing him to the ground, instead of McGraw.

The officers are now under investigation for failing to restrain or immediately arrest McGraw.

"The police jumped on me like I was the one swinging," Jones told the Washington Post. "My eye still hurts. It's just shocking. It's like this dude really hit me and they let him get away with it. I was basically in police custody and got hit.''

The internal department investigation was announced at a press conference by Cumberland County Sheriff Earl Butler.

"No one should be subjected to such a cowardly, unprovoked act as that committed by McGraw," said Butler. "Regardless of political affiliation, speech, race, national origin, colour, gender, bad reputation, prior acts, or political demonstration, no other citizen has the right to assault another person or to act in such a way as this defendant did."

But Sergeant Sean Swain told the Wall Street Journal that the police officers did not notice the attack because they were looking at the stairs along the stands, and that Jones may have "tripped."

"We should have done exactly what we did,'' the sergeant said. "We didn't hurt anybody. We did what the Secret Service asked us to do and separate everybody. If you don't separate and extinguish the problem right there as it occurs, it gets worse. It can escalate so fast it's hard to control.''

Trump rallies are often raucous and chaotic, and because the events are privately booked it is up to Trump to order who gets to stay and who must leave. In February he ordered 30 black students — who were not protesting — to be removed from their stadium, which he had rented, at the University of Valdosta in Georgia.

McGraw appears to be the only Trump supporter to be charged with assault over the last several months despite a number of videos at various campaign rallies showing attacks on African-Americans or other minorities at Trump rallies. Trump has promised to pay the legal fees of anyone "roughing up" a protester.