On Saturday the US President was filmed by reporters looking confused and fumbling for notes to answer a reporter's question on claims of Russian cyber-attacks. The scene has led Republican member of the House of Representatives Ronny Jackson to demand that Mr Biden receive a test of his cognitive fitness. Mr Jackson was also Donald Trump's former White House doctor.

       The doctor is demanding that Mr Biden take the same cognitive test that was passed by Mr Trump when he was 75.

       The test in question is called the Montreal Cognitive Assessment (MoCA) to test for memory impairment, dementia, and other possible maladies.

       Mr Jackson appeared on Fox News on Saturday evening and referring to Mr Biden said: "I think he's demonstrating every single day that there is something going on.

       "You don't need to be a physician to look at this behaviour and see there's something concerning happening.

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       "He's just not ageing gracefully at this point."

       On the occasion, a reporter surprised Mr Biden outside a US store and said: "With the most recent hack by the Russians, would you say that this means?"

       However, Mr Biden fumbled and read a piece of paper from his pocket then slowly responded: "We're not sure it's the Russians."

       He added: "I got a brief when I was on the plane.

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       "That's why I was late getting off the plane."

       Mr Biden then paused and finished by saying: "I'll be in better shape to talk to you about it..."

       Then Mr Biden appeared to be considering replying to a cashier from the shop he was standing outside, but he then decided to continue his conversation with the reporter.

       He added: "The idea, first of all, we're not sure who it is for certain, number one.

       "And what I did, I directed the full resources of the government to assist in a response if we determine, what else you need?

       "I directed the intelligence community to give me a deep dive on what's happened.

       "I'll know better tomorrow."

       The 78-year-old President was coming out of King Orchards farm store in Central Lake, Michigan on Saturday when he was asked the question.