It’s a curious time to discussing anyone else’s inability to serve as president of the United States, when Donald Trump has resorted to Twitter to tout his own “great and unmatched wisdom” about foreign policy without a hint of irony.

But it’s time nonetheless: We can’t be serious about Bernie Sanders prospectively being president until he’s 87 years old or Joe Biden until he’s 86.

Anyone who has helped care for truly elderly parents knows this.

Many much-older parents — including 95-year-old former President Jimmy Carter, who said last month he couldn’t have done the job at 80 — know it, too.

But we have to talk about it now, with Sanders having had a heart attack last week and Biden struggling daily to defend his integrity against wholly made-up attacks by President Donald Trump. As adult children say to more-ordinary parents than Sanders, Biden or Trump, about more-mundane matters like driver’s licenses and cooking for themselves, it’s time.

I speak from — perhaps over-extrapolate from — my experience as a son whose mother died from dementia complications in 2014. My siblings and I had The Talk with each other around my brother’s dining-room table just after Christmas 2006, and should have had it sooner.

Mom’s death was long and hard, and while not without its own beauty it’s something you’d never wish on anyone. Things that happen weeks apart for other patients — not recognizing people, losing the ability to focus on tasks, ceding the capacity to walk unaided — happened months or years apart for my mother.

All along the way, the seven of us — six, after we lost my sister to cancer — denied what we were seeing, hoped things would improve or at least progress more slowly. Each of us in a mix of our own mind’s creation. People do this.

Lying, concealing, denying

And do it without the incentives that presidential administrations have to lie (beginning with lying to themselves), conceal, or otherwise obscure the principal’s bad health so an administration’s agenda can move forward.

Given the awesome responsibilities of the presidency, it’s naive not to talk about it.

The health issue need not be Alzheimer’s or dementia. The large number of sufferers doesn’t even include those who are simply not as quick or as intellectually nimble as they once were — signs we see in all three of the oldest presidential candidates, including Trump, if we’re honest.

We know White Houses do this. Nixon’s covered up his drinking. Franklin Roosevelt’s staff hid his wartime decline into heart failure. John Kennedy’s team concealed his Addison’s disease. Doubts about Ronald Reagan, who died of Alzheimer’s, pervaded Washington throughout his second term.

In the granddaddy of them all, Woodrow Wilson’s wife moved heaven and earth for more than a year to keep the world from discovering how fully the 28th president was disabled by a stroke.

Tough math

Somewhere between one in six and one in four people in their 80s get dementia, according to different sources. Almost one in three presidencies since 1900 have been marred by concealment of serious, debilitating presidential illness (not even counting Dwight Eisenhower’s coverup of the severity of his 1955 heart attack, or speculating about Trump’s mental health).

It’s tough math, but the calculations need to be made, and realistically.

The life expectancy of an 80-year old U.S. male is eight years, the length of two presidential terms, according to the Social Security Administration. If Alzheimer’s doesn’t crop up, it could well be something else. And that’s without the stress of the presidency.

Yes, we all know of people who work successfully into their 80s. Warren Buffett is an extreme example, pounding steaks and Cherry Cokes and running Berkshire Hathaway at 89. But even Buffett has made no bones about Berkshire being run by heads of its operating companies, with headquarters staff making investment decisions — relying, increasingly, on younger executives for those.

If there’s one thing we consistently don’t know, even about our loved ones, it’s when their existing faults (Biden’s loopiness, Sanders’ unwillingness to recognize when opponents make a good point, Trump’s determination not to read) blend into a permanent, age-related problem. If they do cross the line, will they recognize it? Will their teams admit it — or, like my siblings and I did, spend years in denial?

Even without age-related decline, the presidency’s no ordinary job. We’ve watched its demands for quick adaptation to changing facts flummox George W. Bush — a Yale and Harvard graduate who was 62 when 2008’s financial crisis hit, and 55 when he decided Saddam Hussein’s Iraq and the terror group al-Qaeda were joined at the hip.

Americans shouldn’t relish even a healthy 85-year-old trying to manage such fast-moving cross-currents of facts and analysis. Biden or Sanders at that age might be better than Trump at 73, but so would a can of tomatoes.

Perfectly good options

Asking these questions becomes easier when there are perfectly viable options.

On the Democratic side, Elizabeth Warren, a very young-seeming 70, has organized the most-effective campaign to date, addressing her perceived flaw as a chilly Harvard academic by emphasizing working-class roots, and developing policy proposals around the clear themes that eluded the younger Hillary Clinton.

There are a half-dozen other plausible presidents. They’re 54 (Kamala Harris), 50 (Cory Booker), 45 (Julian Castro), 47 (Beto O’Rourke), and 59 (Amy Klobuchar) — and 37-year old Pete Buttigieg.

It’s too soon to know whether pressure to step aside after his heart attack will drive Sanders from the race, or whether early primary-state voters will force Biden’s hand.

But we know what it looks like when a president manifestly can’t handle the job — can’t master or retain the material, can’t weigh pros and cons meaningfully, grunts instead of thinks. That’s Trump.

It’s a hell of a chance for us to take — again.