Voters have been raising concerns about Joe Biden's age since he launched his 2019 bid for President at age 77.
But doctors tell DailyMail.com an alarming deterioration began in 2021.
After his disastrous performance in last week's debate, many have been left wondering how long the now-81-year-old's faculties have been diminished — and how long his team has known about it.
We asked several doctors to review a Mail time-lapse of the ailing President over the decades and also to consider his public appearances.
The consensus was that there was a sharp decline both in his appearance and cognitive abilities beginning in 2021, according to the experts, who spoke on and off the record due to lingering fears their comments could cause reputational damage.
They told this website the photos revealed a 'glassy', vacant look in Biden's eyes as well as 'blank' facial expression andpaler skinbeginning around three years ago.
Biden at a Democratic nominee debate in 2019 looking sharp (left) and the ailing president in 2024
Dr Stuart Fischer, an emergency medicine physician in New York City, said: 'Reviewing all these photos of Joe Biden, the only unqualified success he has had is his hair transplant — it still looks great!
'But from 2021 onwards, there is a shift in the expression in his eyes — he starts to look a bit like a zombie — which has a blank stare.
'This is particularly evident in June 2023 with Vice President Harris, where he starts to look blank and stops moving, which has alarmed people.'
He added: 'People decline at different rates normally, and in their 80s you would expect to see some sort of decline.
'But at 81 years old he is youngish to have such severe problems. If you think of Mick Jagger who is 80 years old, for example, he is still performing on stage with ease.'
President Biden had the classic signs of aging in the late 2000s and early 2010s when he was vice president to Barack Obama, the experts said.
He had bags and grooves under his eyes, a receding hairline and sagging skin, to name just a few features.
But the doctors DailyMail.com spoke to said that around 2019, when Biden was preparing for his successful presidential run, his face transformed.
The doctors DailyMail.com spoke to said Biden had been aging normally up until 2021/2022 - when the decline became sharper
His skin appeared much tighter, which they said was likely due to plastic surgeries including a facelift and treatments with filler.
Dr Smita Ramanadham, a plastic surgeon in New Jersey, said: 'There appears to be a battle going on with Biden, where he is aging and his team are trying to counteract that [the rapid aging and frailty] with various treatments.
'All the treatments he has had mean he no longer really shows his emotions below the eyes, which can make it difficult to establish what is going on internally because his emotions are not clearly displayed on his face.'
Dr Ramanadham said she too noticed a change in 2021 — this time with the president appearing much older and frailer.
She said: 'Observing the eyes and the expression around them, they do appear to have a glassy and foggy type of appearance in later images. They also have this wide-openness.
'On his skin, over time it also appears to lose color — which is a sign of [advanced] aging.'
She added that it was also important to consider his movements, as well as his expressions.
Dr Ramanadham said: 'If you just watch him, he is moving a little bit slower and he is slower to respond too, you can see him almost processing the information and sometimes there is this glazed blank look too.
Biden looking slick in 1991 versus at last week's debate against Donald Trump, which could prove to be the downfall of his presidency
'I think this is what is triggering all the questions about his candidacy.'
Many doctors have suggested privately to DailyMail.com that he is likely suffering from some sort of condition, rather than just aging.
The White House has downplayed suggestions that Biden is suffering from neurological issues, claiming the President simply had a 'bad night' and was suffering from 'a cold'.
The WH has said, however, that Biden functions perfectly well during the hours of 11am and 8pm, but can become gaffe-prone later in the evening.
Seven in ten voters now say that they do not think Biden is mentally fit to serve as President - compared to around half who think the same about Trump.
Dr Sanjay Gupta, chief medical correspondent atCNN, todaycalled for Biden to undergo a cognitive test in a sign that even corners of the media normally friendly to the president are turning.
He wrote: 'For me as a brain specialist, it was concerning to watch President Joe Biden, and it quickly became clear that I was not along in my reaction.
'We often hear that observing a candidate on the campaign trail is the best assessment of the individual’s physical and cognitive health.
'The country is watching now, and that assessment gives cause for concern — and a need for transparent testing.'
Biden in his heyday (left) and a video of the president with a blank stare on the White House lawn last month which sparked concern
Many doctors are calling for Biden to take the Montreal Cognitive Assessment, or MoCA, a screening test used to pick up concerning cognitive decline.
It is the test that Trump has taken twice and says he aced both times, scoring a 30 out of 30.
The test's creator, Dr Ziad Nasreddine from Canada, has also called on Biden to take the assessment — telling DailyMail.com he couldn't keep silent after watching him in the debate last month.
It comes as the ailing president goes into a 'make or break' weekend of campaigning while his presidential bid teeters on a knife edge.
Reports from anonymous sources say that Biden is aware that if he messes up the events then he will reconsider his decision to run in the race.
