White House aides appear to have inadvertently confirmed that President Joe Biden is suffering from a condition that is linked to dementia and Alzheimer’s disease, Axios is reporting.

When President Biden and former President Donald Trump met on the debate stage, Biden became the focus as he appeared confused, froze up, and stumbled through answers. Amid calls for the 81-year-old to drop out of the race, the Biden campaign and the president have worked to dispel concerns, downplaying the performance as a rough night. Despite the damage control, sources told Axios that Biden is “dependably engaged” between 10 a.m. and 4 p.m. but is susceptible to “verbal miscues” and fatigue outside that timeframe.

Throughout Biden’s presidency, aides have observed “flashes of an absent-minded Biden” but have typically dismissed these instances because the president is generally engaged, according to eight current and former Biden officials who spoke with Axios. The time of day significantly influences Biden’s performance during his duties as president, the outlet reported.

“Some campaign aides projected calm Friday and framed the debate as just a bad night that they’d recover from. Other Biden aides, donors and senior Democrats were deeply shaken, as Trump and other crowing Republicans questioned his fitness for office,” Axios reported. “Beyond the politics of whether Biden can beat Trump again, the aides expressed new worries about whether the president can carry out his duties through another four-year term.”

“The time of day is important as to which of the two Bidens will appear,” Axios reported after speaking with White House staff. “From 10am to 4pm, Biden is dependably engaged — and many of his public events in front of cameras are held within those hours.” Aides told the outlet: “Outside of that time range or while traveling abroad, Biden is more likely to have verbal miscues and become fatigued.” It’s important to recall that the debate with Trump began at 9 p.m. EDT.

The behavior described by Biden’s aides can be likened to a symptom of dementia known as “sundowning,” which refers to a state of confusion that particularly affects elderly individuals, especially those with Alzheimer’s disease or other forms of dementia, during the evening or as the sun is setting, according to the Mayo Clinic. In more severe instances, “sundowning” can lead to anxiety, aggression, pacing, wandering, hallucinations, and sleep disturbances, as stated by the Mayo Clinic.

Despite concerns about Biden’s age, the current White House physician determined in February that Biden was fit for office after conducting a physical examination. Dr. Kevin O’Connor concluded in a report that Biden was an “active” 81-year-old and able to execute his duties as president.

“[There] is one Joe Biden, who works his heart out fighting for families like the one he grew up in, in Scranton, and who, because of his determination, experience, and decency, keeps achieving unprecedented results for them,” White House deputy press secretary Andrew Bates told Axios.