A Georgetown University professor said Donald Trump is engaging in "retroactive bigotry" when he questions President Obama’s intelligence and background and called on Republicans to either embrace Trump or distance themselves.

"This is racism by inference," Eric Dyson, a prominent African-American academic, said on CBS' “Face the Nation.”  “Skepticism about black intelligence and suspicion about black humanity have gone hand in hand throughout the history of this country in feeding the perception that black people don't quite measure up."

Dyson pointed out some of Obama’s academic accolades, including graduating magna cum laude from Harvard Law School and also being the first African-American to edit the Harvard Law Review.

He called Obama’s academic credentials “unimpeachable.”

“The reality is that Barack Obama has been called to account by a man who has nothing near the intellectual credibility or the social standing that the president has,” Dyson said during the interview.

On Friday, Trump called “our leaders” stupid. The real estate mogul has also questioned Obama’s college record.

“The word is [the president] wasn't a good student and he ended up getting into Columbia and Harvard,” Trump recently said.  “I'd like to know, how does he get into Harvard? How does he get into Columbia if he isn't a good student?"

Trump has been critical of Obama, saying he will go down as the worst president in history.

Dyson said, “We (African-Americans) are constantly questioned as to our legitimacy - whether we belong or not - and Barack Obama is our big brother in that case. ... An assault on him is an assault on everybody.”