FIRST ON FOX: After President Joe Biden’s announcement on Sunday that he is dropping out of the 2024 presidential race, two doctors shared thoughts with Fox News Digital about what this means in terms of Biden's ongoing cognitive health. 

Looking back, some experts believe the path to Biden’s dropout began with what was widely described as a disastrous debate performance in late June, during which the president seemed to display an unclear train of thought and a lack of coherence.

"President Biden has shown signs of cognitive impairment for many years," Dr. Brett Osborn, a Florida neurosurgeon who specializes in cognitive function, told Fox News Digital on Sunday. He has not treated Biden or advised him. 

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"It is medically probable that when he took office in 2020, he was afflicted by mild cognitive impairment (MCI), a gateway syndrome to Alzheimer’s disease and potentially Parkinsonism (not necessarily Parkinson’s disease itself)," Osborn said. 

"And he has only deteriorated since then, as is typical of those with neurodegenerative diseases."

Given signs of his "ailing cognitive status, President Biden's decision to step down from the race seems prudent," said Osborn, expressing his professional opinion.

"In my opinion, he is unfit to run the country and is unsuitable for his duties as commander-in-chief," he said.

"By stepping down, President Biden can prioritize his health and potentially mitigate further cognitive decline, while also ensuring the leadership role is filled by someone fully capable of handling the demanding responsibilities of the position."

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Dr. Marc Siegel, clinical professor of medicine at NYU Langone Medical Center and a Fox News medical contributor, said he believes Biden’s decision is best for the president’s health.

"The stress of the race could have definitely made cognition worse — but it will progress anyway, and fitness is a big concern," the doctor told Fox News Digital on Sunday. He has not examined or treated Biden. 

Osborn also emphasized that remaining in the presidential race could have been "detrimental" to Biden's mental and physical health. 

"Chronic stress releases cortisol, the dominant stress hormone of the body, which can negatively impact the frontal and temporal lobes of the brain, leading to further deterioration," Osborn told Fox News Digital.

Biden’s past brain surgeries could also have affected his cognitive function, according to Osborn.

"It is likely that the combination of the two brain surgeries and his [possible] neurodegenerative diseases, plus the added stress of the Oval Office, have markedly accelerated the deterioration of his already ailing brain," he said.

"Another term [was] not even a consideration, in my opinion. By 2028, he will categorically be a ‘nursing home patient.’"

In addition to cognitive concerns, the doctors also discussed Biden’s recent bout with COVID-19.

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"Post-COVID syndromes and long COVID have been shown to affect underlying neurological conditions," Siegel warned. 

"This can also come from recurrent COVID."

Regarding COVID, Osborn noted that the virus has been shown to have potential long-term effects on cognitive function, often referred to as "brain fog." 

"These effects can include difficulties with memory, attention and executive function," he said. 

"In someone with pre-existing cognitive issues like President Biden, contracting COVID-19 could exacerbate these symptoms – via neuroinflammation – and lead to a more rapid decline."

Osborn also suggested that the president’s contracting COVID was used as an "exit strategy."

"It accelerated his, but more likely their, decision to vacate his run for the presidency," the doctor surmised.

Along with meeting the official requirements — that the president must be a natural-born citizen, must be at least 35 years of age, and must have lived in the country for at least 14 years — both doctors agreed that the individual should also be physically and cognitively healthy.

"It is extremely important," Siegel told Fox News Digital. "We have a right to it as a country."

The role of president involves making complex and high-stakes decisions, often under significant pressure, Osborn noted. 

"Cognitive health is essential for clear thinking, effective communication and sound decision-making, all things President Biden lacks," he said, sharing his viewpoint. 

Physical health is also essential, Osborn said, as the role also requires long hours, frequent travel and crisis management.

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"A healthy president is better equipped to handle the demands of the office and to lead the nation effectively through various challenges," he added.

In light of Biden’s announcement to exit the race, Siegel said the decision "should be accompanied by a full health disclosure."

He said, "They should admit to what they know and reveal full neurological results."

The situation highlights the need for thorough health evaluations for presidential candidates – and sitting presidents — to ensure they can perform their required duties, according to Osborn. 

"Routine testing – physical and mental – should be made non-negotiable instead of being thwarted by the governing party," he said. 

"The allowance of President Biden’s mental incompetence for four years is an embarrassment to the United States government, and the world has borne witness."

In response to outreach from Fox News Digital, the White House press office stated that "health was not a factor" in the president's decision to withdraw from the race. 

"He looks forward to finishing his term and delivering more historic results for the American people," said the White House in its statement. 

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On July 21, the White House released the most recent health update from the president's physician, Dr. Kevin C. O'Connor.

O'Connor also noted that Biden is continuing his course of Paxlovid and that his COVID symptoms have "significantly" improved. The doctor also stated that Biden's vital signs are normal, and his lungs remain clear.