Last Thursday was not a good day for Joe Biden. During the president’s shaky and at times incoherent debate performance, he appeared weaker and frailer in real time than the American public had ever seen. Friday appears to have been a much better day. At a campaign rally in North Carolina, clips of which his campaign distributed online, the president seemed like an entirely different man. Lively and invigorated, he spoke with a ferocity that had eluded him on the debate stage.
Both his supporters and detractors have turned this yo-yoing into a talking point that has come up frequently in the days since the debate: The president has good days and bad days. Biden himself has said that he “didn’t have my best debate night,” and his press secretary spun the performance as the result of a cold rather than “an episode.” Indeed, earlier this year, at the State of the Union, Biden appeared much more lucid.
Many people have pointed to Biden’s inconsistencies as indicative of something more serious, and the challenge—perhaps the insurmountable challenge for the White House—is that it is unclear which version of Biden will show up next. The president is slated to appear in an interview with ABC’s George Stephanopoulos on Friday, and as The New York Times reported earlier today, Biden understands that another bad performance may doom his candidacy. There are many reasons a person could swing between good days and bad days. Some of them are benign. Some of them are threatening a presidency.
At 81, some cognitive unevenness is to be expected. It’s also to be expected for Donald Trump, who is 78. The brain slows down as a person gets older, Steven P. Woods, a psychology professor at the University of Houston, told me. Learning and remembering don’t come as easily as they used to. Flubbing a word here or there is one thing. But executive functioning—higher-order processes that enable planning and cognitive flexibility—tends to decline too. As a result, cognition becomes less consistent. The notion of good versus bad days falls under a scientific category encompassing spontaneous changes in attention and consciousness: cognitive fluctuations. As people get older, they may experience more frequent and more significant fluctuations than before. Parts of the brain involved in learning and complex functions can shrink, and communication among certain neurons can break down.
The big question, Woods said, is “what happens when fluctuations become abnormal?” What constitutes unusual cognitive variability depends entirely on the person’s overall health. A brief decline in energy or focus isn’t, on its own, a cause for concern, Woods said. Needing the occasional nap would not by itself render someone unfit for the nation’s highest office. But it could be a problem if accompanied by consistent cognitive shifts, significant medical changes, or impairments to daily life. “If you have a fluctuation where you’re no longer able to manage your day-to-day, even for a period of time, that would be abnormal to me,” Jeremy Pruzin, a cognitive-behavioral neurologist at Banner Alzheimer’s Institute, told me.
Not all fluctuations caused by aging are that severe. But age is a risk factor for conditions that can worsen fluctuations, such as dementia and neurodegenerative diseases. Brain trauma, certain infectious diseases, and mood disorders are also associated with those changes. Fluctuation can take place within days, not just between them: Sundowning, largely associated with Alzheimer’s disease, refers to cognitive issues that arise in the late afternoon and early evening.
A bad day can be part of a constellation of symptoms. In people with Parkinson’s disease, for example, cognitive fluctuations can accompany a soft voice, a shuffling gait, an inability to move fluidly, and a decrease in facial expression, Pruzin said. Cognitive fluctuations are also the cardinal feature of Lewy body disease, a type of dementia. According to Pruzin, people with this illness can “seem rather out of it for periods of time, then seemingly back to or close to normal within the course of hours or a day.”
Biden has not reported having any of these ailments. After an annual physical in February, the president’s doctor said he was “fit for duty,” though Biden was not administered a cognitive test. But after last week, it’s entirely understandable that many Americans are asking whether something more serious is wrong with the president.
Biden’s cognitive variability isn’t necessarily a sign of illness, or even old age. “We all experience good days and bad days,” regardless of age, Alexandra Fiocco, a psychology professor at Toronto Metropolitan University, told me. People misplace their coffee cups, forget the names of their colleagues, stare blankly at laptops. Nobody can be “on” all the time. Fluctuations are just part of “normal human cognition,” Woods said.
External factors, such as lack of sleep, low physical activity, high stress, and certain prescription medications, can play a role. The effects of a spoiled tuna sandwich or a bad breakup can easily derail cognition. Some people naturally experience more fluctuations than others—psychologists call this “intra-individual variability”—owing to many variables, including differences in biology and brain pathology.
Unfortunately for voters, there are more questions than answers about what caused Biden’s bad night. You can’t gauge cognitive variability based on a few media appearances, or even a prolonged debate. Usually, doing so requires a battery of tests and long-term observation. There is a tendency to assume that older adults have dementia when less dire factors, such as lack of sleep and dehydration, may be at play, Fiocco told me. It takes the whole picture “to determine whether somebody’s just having a bad day, or if this dramatic bad day is part of a broader syndrome related to a disease,” Pruzin noted.
The public’s skepticism about Biden’s health is understandable. U.S. presidents have a record of keeping Americans in the dark about their health woes. See also: Grover Cleveland, Woodrow Wilson, and Franklin D. Roosevelt. Certainly, it’s possible that Biden didn’t get enough sleep, was especially stressed, or was impaired by a cold, as his team said last Thursday. But that possibility can coexist with another: He is just old.
