I have been a fan of Joe Biden since the days when he served as Barack Obama’s vice-president.

Throughout those two presidential terms Biden was loyal, collegial and Obama’s bridge to Congress. Before the vice-presidency, he served in the senate where he was liked and trusted by colleagues on both sides of the aisle and was known for his gaffes and faltering speech.

Politically, he was the working man’s candidate who could be counted on to deliver battleground states, which helped Biden beat Trump four years ago. 

And he might have repeated this time were it not for his increasingly frail appearance and sometimes halting, slurred speech.

All of which were on full display and much worse in his first presidential debate with Trump. That evening, he frequently mumbled, struggled to find words, several times lost the thread of what he wanted to say and even the words, and looked blank, much as Mitch McConnell, the Senate minority leader, had famously looked more than a year ago.

Leadership of any government is tough, but the presidency of the United States is perhaps the toughest — long, wilting hours, reaching tough decisions, developing consensus, showing leadership when it’s needed and juggling so many active policy files and much, more with no let up for four solid years. 

The job demands the full attention of the president, great stamina, focus, thoughtful analysis of issues, judgment, flexibility and working with all kinds of people every day.

The sweet spot for the job is probably between late 40s and mid-60s, when presidents have acquired sufficient experience and possess the cognitive wherewithal to learn and manage the job effectively.

And it’s not so late in their career that learning, memory and focus become more effortful, and stamina begins to wane.

Aging can be looked at in three phases. The first from before birth to the late 20s and early 30s is the period when learning in many fields is most easily accomplished and there are few impediments to acquiring new cognitive and motor skills.

The mid period, between the early 30s and early 60s, is a one of consolidation and additive learning, but perhaps not with the same facility as in the first third of life.

The last third of life is associated with slowing of almost all cognitive functions, especially toward the late 60s and early 70s, when the earliest hints of cognitive impairment begin to register on psychological tests.

These become much more common and severe in the 80s, when physical impairments increase and up to 50 per cent have significant cognitive impairments.

Such simple staging is supported by MRI studies, which reveal the earliest declines in the thickness of the neocortex by the late 20s, with atrophy of the brain beginning in the 30s and growing much more obvious in the last third of life.

The brain, like every other organ and system in the body, begins to show signs of aging in mid-life including age-related shortening of chromosomes, the accumulation of mutations in DNA, epigenetic modifications to genes and age-related changes in other components and systems in cells. 

Returning to Biden, my sense is that if cognitive tests were carried out now, he would not fare well. He will be 82 in November and 86 had he stayed for a second term.

What we’ve witnessed of his frailty and cognitive impairments in his first term will surely progress. True, staff can help a lot, but they shouldn’t be counted on to make presidential decisions.

In conversations about Biden, there’s little talk about what any neurologist or psychologist would want to do: apply the same standards to him as they would anyone else.

Indeed more so, since U.S. presidents should be held to higher cognitive standards given the challenges of the job and the public has a right to know about his competency for office. No one Biden’s age is allowed to be an airline pilot and no one 80 and over should be allowed to be president. 

Biden isn’t the only one. What about senators Feinstein and McConnell, who share similar issues. Or Trump, whose increasingly unhinged tirades about this or that person or institution suggest progressive loss of emotional control as sometimes happens with frontal lobe degenerative diseases. 

We should be concerned that there are no statutory requirement age limits for such high offices and no mandatory neuropsychological assessments even when the stakes are so high. 

Competency for pilots and physicians is regularly assessed. Why not presidents and other senior leaders?

The fact that Biden announced on July 21 he will not seek re-election is a relief for the U.S. and for him. That took courage but was the right decision given the trajectory of where his disease is headed in the next several years.

Biden made the right decision and I hope the lesson will not go unnoticed for others in similar circumstances.