Former Trump campaign aide Sam Nunberg was once ordered to break down the American Constitution for Donald Trump at the outset of his 2016 presidential campaign, according to a new book about the president's journey from billionaire real estate developer to commander-in-chief.

Nunberg told veteran journalist Michael Wolff that "early in the campaign, [he] was sent to explain the Constitution to the candidate."

"I got as far as the Fourth Amendment before his finger is pulling down on his lip and his eyes are rolling back in his head," said Nunberg, who was fired by Trump just two months after he launched his campaign.

His claim was published Wednesday as part of an excerpt from Wolff's forthcoming book, "Fire and Fury: Inside the Trump White House," which is due for release on Jan. 9.

The civics lesson Trump was allegedly forced to endure isn't the first time his knowledge of the Constitution has faced scrutiny.

During a meeting with Republican lawmakers that took place months before the presidential election, Trump reportedly vowed to protect a non-existent article of the Constitution.

"I wasn't particularly impressed," Congressman Mark Sanford, R-S.C., had told The Washington Post after the meeting. "At one point, somebody asked about Article I powers: What will you do to protect them? I think his response was, 'I want to protect Article I, Article II, Article XII,' going down the list."

"There is no Article XII," Sanford noted.

Trump has also criticized the system of checks and balances incorporated in the Constitution, once calling it a "rough" and "archaic" system that is "really a bad thing for the country."