Fears for Donald Trump's health have once again reared their head as the author of an explosive biography suggested his condition is "like a black box". The 80-year-old leader's cognitive and physical abilities have come under increased scrutiny in recent months following a series of public gaffes and apparent bruising and swelling.

Commentary around his capacity to remain in office was given fresh momentum by the release of a biography by two former New York Times journalists last month. Maggie Haberman and Jonathan Swan claimed the president is nocturnal and unpredictable and has shown increasing "moments of fatigue" during his second term in Regime Change: Inside the Imperial Presidency of Donald Trump.

Ms Haberman poked the bear further in an interview with MSNOW over the weekend, telling them Mr Trump's health "is like a black box inside that administration" and suggesting its obscurity may have led to "an area of failure in the reporting".

Mr Trump hit out at Ms Haberman in a lengthy Truth Social post just hours before the interview, labelling her "Maggot Hagerman" and accusing her of "bad reporting".

"Maggot Hagerman has covered me incorrectly for ten years," he wrote. "She has made a living off her bad reporting, and will pay the price when our Multi Billion Dollar Lawsuit against The Failing New York Times gets to court."

He went on to defend his health, insisting a recent physical examination had proven him once again to be in a "perfect" state.

"I just finished a perfect physical at Walter Reed [National Military Medical Centre], I do it every six months, and I requested another Cognitive Test, the only President to do so, three times, and I aced them all," Mr Trump said.

"Few people in Washington DC could do so, including Maggot and her flunky associate, Jonathan Swan."

Responding to the jibe, Mr Swan wrote in a post on X: "I would be honoured to do another on-camera interview with President Trump whenever he wants."

He also shared a photo of Regime Change topping Amazon's bestseller charts, alongside the message: "Many people disagree with the president's assessment. Thanks to you all for reading."

White House physician Sean Barbarella has echoed Mr Trump's verdict on his health, insisting that his recent medical exams show he is "fully fit" with "strong cardiac, pulmonary, neurological and overall physical function".