Joe Biden’s brain surgeon said his former patient is “totally in the clear” as speculation over the candidate’s health -- with Biden possibly becoming the oldest president in U.S. history -- is likely to become a campaign issue.

The former vice president, who had been perceived by many as the strongest potential contender for the Democratic Party's 2020 presidential nomination, formally announced his candidacy Thursday.

But Biden’s age – 76 – is expected to become a source of attacks from a younger generation of Democrats not because of obvious generational differences, but possibly for actual health concerns if Biden gets into office.

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Biden himself agreed last year that “it's totally legitimate” for people to ask questions about his health if he decides to run for president, given his medical history -- which has included brain surgery in 1988.

“I think they're gonna judge me on my vitality,” Biden told “CBS This Morning.” “Can I still run up the steps of Air Force Two? Am I still in good shape? Am I – do I have all my faculties? Am I energetic? I think it's totally legitimate people ask those questions."

"I think they're gonna judge me on my vitality. ... I think it's totally legitimate [that] people ask those questions." — Joe Biden

But Dr. Neal Kassell, the neurosurgeon who operated on Biden for an aneurysm three decades ago, told the Washington Examiner that Biden appears to be “totally in the clear” -- and even joked that the operation made Biden "better than how he was.”

“Joe Biden of all of the politicians in Washington is the only one that I’m certain has a brain, because I have seen it,” Kassell said. “That’s more than I can say about all the other candidates or the incumbents.”

“Joe Biden of all of the politicians in Washington is the only one that I’m certain has a brain, because I have seen it.” — Dr. Neal Kassell

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At the same time, however, Biden hasn’t been forthcoming about his health at least since 2008 when he released his medical records as a vice presidential candidate. The disclosure that time revealed some fairly minor issues such as an irregular heartbeat in addition to detailing previous operations, including removing a benign polyp during a colonoscopy in 1996, the outlet reported.

It remains unclear if Biden had more aneurysms. Some medical experts say that people who have had an aneurysm can have another one.

An aneurysm, or a weakening of an artery wall, can lead to a rupture and internal bleeding, potentially placing a patient's life in jeopardy.

Biden won’t be the only Democrat grappling with old age. Sen. Bernie Sanders, another 2020 frontrunner, is currently 77 years old and agreed with Biden last year that their ages will be an issue in the race.

“It’s part of a discussion, but it has to be part of an overall view of what somebody is and what somebody has accomplished,” Sanders told Politico.

“Look, you’ve got people who are 50 years of age who are not well, right? You’ve got people who are 90 years of age who are going to work every day, doing excellent work. And obviously, age is a factor. But it depends on the overall health and wellbeing of the individual.”

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Sanders released his medical records in 2016, with a Senate physician saying in a letter that the senator was “in overall very good health.”