US President Joe Biden has hit back after an investigator said he wouldn’t be charged for mishandling classified documents, partly because of his age and failing memory.

Special Counsel Robert Hur released a damning 390-page report on Friday (Australian time) into an investigations into documents about national security issues that Biden took when he left the vice-presidency in 2017.

Hur said he had opted against bringing criminal charges after his 15-month investigation because Biden co-operated and – in a scathing assessment – would likely be difficult to convict.

“We have also considered that, at trial, Mr Biden would likely present himself to a jury, as he did during our interview of him, as a sympathetic, well-meaning, elderly man with a poor memory,” Hur wrote.

“It would be difficult to convince a jury that they should convict him – by then a former president well into his 80s – of a serious felony that requires a mental state of wilfulness.”

Hur said during interviews that 81-year-old Biden was unable to recall the years of his term as vice-president under Barack Obama. Nor could he say to within several years when his son, Beau, died.

Biden defended himself at a testy White House press conference called  in the hours later.

“There’s some attention paid to some language in the report about my recollection of events. There’s even reference that I don’t remember when my son died. How in the hell dare he raise that?” he said.

“Let me tell you something … I don’t need anyone to remind me when he passed away, or that he passed away.”

Tweet from @joehagansays

Biden said he was interviewed on October 8, the day after the Hamas attacks in Israel.

“The simple truth is, I sat for five hours over two days of events going back 40 years. At the same time I was managing an international
crisis,” he said.

“The task was to make a decision about whether to move forward with charges in this case. That was their decision to make. That is his job. And they decided not to move forward. Any extraneous commentary, they do not know what they are talking about.”

As journalists shouted questions at him about Hur’s description, including whether he should continue as President, Biden agreed he was elderly.

“I am an elderly man and I know what the hell I am doing. I am the President and I have put this country back on its feet,” he said.

Unfortunately for Biden, he then went on to mistakenly refer to Egyptian leader Abdel Fattah El-Sisi as the “president of Mexico” in questions about Gaza.

“I think as you know initially, the president of Mexico, El-Sisi, did not want to open up the gate to humanitarian material to get in. I talked to him. I convinced him to open the gate,” he said.

As the clip was shared widely on social media, Republicans seized on it as more evidence Biden was not up to the job of president.

“Weak and sad,” Trump campaign senior adviser Chris LaCivita wrote on X.

“Nothing to see here. Nothing at all,” Trump adviser Jason Miller wrote.

Tweet from @LaCivitaC

Earlier, Alex Pfeiffer, the communications director of the pro-Trump organisation Make America Great Again Inc, had declared: “If you’re too senile to stand trial, then you’re too senile to be president. Joe Biden is unfit to lead this nation.”

Hur found that Biden took a handwritten memo to then-president Obama in 2009 opposing a planned troop surge in Afghanistan, and handwritten notes about intelligence briefings and national security meetings.

Hur’s report found that Biden read aloud classified notebook passages to his ghostwriter at least three times, recounting meetings in the White House Situation Room.

The ghostwriter deleted audio recordings of his conversations with Biden after learning about the special counsel’s investigation but kept transcripts, Hur said.

Hur wrote that Biden’s actions “present serious risks to national security, given the vulnerability of extraordinarily sensitive information to loss or compromise to America’s adversaries”.

But he said the documents might have been taken to Biden’s home while he was vice-president, when he had the authority to do so.

Hur said Biden would not have faced charges, even without a long-standing Justice Department policy against indicting a sitting president.

The conclusion ensures that Biden, unlike his expected 2024 presidential rival Donald Trump, will not risk prison time for mishandling sensitive government documents.

Trump has described the four criminal prosecutions he faces, including one for his handling of classified documents, as politically motivated. He has claimed, without evidence, that Biden is behind the cases.

Trump faces a 40-count federal indictment for retaining highly sensitive national security documents at his Florida resort after leaving office in 2021 and obstructing US government efforts to retrieve them.

He has pleaded not guilty and accused prosecutors of political motivations. A trial is scheduled for May.

-with AAP