"The American Academy of Neurology has estimated that at least 15 percent of those over the age of 75 have some cognitive impairment, a significant number. And several studies reveal that many of those who underwent an open surgical brain aneurysm repair or had a subarachnoid hemorrhage can develop cognitive difficulties as a result. (Biden had two such repairs and a brain bleed in 1988, years before modern endovascular techniques that cause minimal damage were introduced.) Not only that, but a study published in the journal Nature Cardiology in 2018 showed a significant increase in cognitive problems in patients with prolonged atrial fibrillation, from which the president also suffers."