Throughout his presidency, critics and the media had questioned Biden's fitness to run the office, pointing to frequent gaffes and what many saw as a decline in his faculties.

Joe Biden’s metastatic prostate cancer diagnosis, coupled with revelations about his decline in recent years, has renewed chatter and anxiety about the former president’s health.

Some Americans say they don’t understand how former President Joseph R. Biden Jr. could have only recently learned that he had an aggressive form of prostate cancer that had already spread to his bone...