Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE’s physician said in a new interview that the former vice president has shown no mental deficits since suffering two brain aneurysms in 1988, challenging concerns surrounding the Democratic White House hopeful's mental fitness.

“Vice President Biden is in excellent physical condition,” Dr. Kevin O’Connor told Politico in a statement. “He is more than capable of handling the rigors of the campaign and the office for which he is running.”

The aneurysms were fully treated, Dr. Neal Kassell, who performed the surgery, told Politico, adding that Biden, now 76, showed no change and no damage in the years afterward.

“He is every bit as sharp as he was 31 years ago. I haven’t seen any change,” Kassell said. “I can tell you with absolute certainty that he had no brain damage, either from the hemorrhage or from the operations that he had. There was no damage whatsoever.”

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Kassell added that he is "going to vote for the candidate who I am absolutely certain has a brain that is functioning."

"And that narrows it down exactly to one,” he said.

Biden has faced skepticism and criticism over his performance in the first round of Democratic primary debates, as well as limited public appearances on the campaign trail, which made some question whether he was able to keep up with his younger competitors.

But after a stronger second debate performance, Democratic lawmakers have since said they feel better about Biden as their party’s White House front-runner, despite lingering questions about his age.

The former vice president is one of a group of older 2020 presidential candidates including 77-year-old Sen. Bernie Sanders Bernie SandersSirota reacts to report of harassment, doxing by Harris supporters Republicans not immune to the malady that hobbled Democrats The Hill's Morning Report - Sponsored by Facebook - Republicans lawmakers rebuke Trump on election MORE (I-Vt.), 70-year-old Sen. Elizabeth Warren Elizabeth WarrenOvernight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds On The Money: Half of states deplete funds for Trump's 0 unemployment expansion | EU appealing ruling in Apple tax case | House Democrats include more aid for airlines in coronavirus package Warren, Khanna request IG investigation into Pentagon's use of coronavirus funds MORE (D-Mass.) and former Massachusetts Gov. Bill Weld William (Bill) WeldRalph Gants, chief justice of Massachusetts supreme court, dies at 65 The Hill's Campaign Report: Biden visits Kenosha | Trump's double-voting suggestion draws fire | Facebook clamps down on election ads Biden picks up endorsements from nearly 100 Republicans MORE, a 74-year-old Republican.

President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE, who has mocked Biden for “not playing with a full deck” and has nicknamed the former vice president “Sleepy Joe,” is 73 years old.