Jackson, said Tuesday that 'as a physician' he believes Biden does not have the 'mental capacity' or 'cognitive ability' to run the country.
I'm pretty familiar with what it takes both physically and cognitively to do that job and what the demands of that job are,' Jackson told reporters on the call organized by the Trump campaign, according to the New York Post.
His comments come one day after Biden's latest gaffe where he appeared to forget Mitt Romney's name.
Trump, who has repeatedly attacked Biden's cognitive abilities and nicknamed him 'sleepy Joe', jumped onto his latest mishaps, and took to Twitter Tuesday morning- insisting that his rival has 'dementia'.
Not as a candidate running for Congress, but as a citizen of this country, I've watched Joe Biden on the campaign trail and I am concerned and convinced that he does not have the mental capacity, the cognitive ability, to serve as our commander-in-chief and our head of state,' he said.
Jackson said he wasn't going to 'diagnose' the Democrat of having dementia or any other condition.
'I'm not trying to remotely diagnose him with anything,' he said.
'I've not accused him of having Alzheimer's or anything of that nature.'
Jackson was nominated to serve as the Secretary of Veteran Affairs in 2018 - a nomination he later stood down from amid amid a flurry of allegations from colleagues about drunken behavior.
The Navy rear admiral went on to say Biden's mistakes are not the 'typical gaffes' he has seen of him over the years.
‘He routinely gets in the middle of a thought and then loses his train of thought and then he can't recalibrate where he's at. He's actually having a lot of trouble recently articulating words.'
'This is a demanding job from a cognitive standpoint, you have to be locked on, you have to be articulate, you have to process lots and lots of information and multitask.'
'And right now he's having a really extreme time just focusing on the one task at hand that he has when he stands up in front of voters and tries to explain something.'
Jackson's medical expertise was called into question back in 2018 when, after carrying out Trump's physical exam, he claimed the president was in 'excellent health' and said if he had a 'healthier diet over the last 20 years, he might live to be 200 years old.'
His positive outlook came despite test results indicating the president had a type of heart disease, worsening cholesterol and coronary calcium levels, and was obese.