Given our rapid demographic shifts, I suppose the problems of an aging society would be embodied in a presidential election eventually. Now they have.

First, we witnessed a president’s dramatic decline in a prime-time presidential debate. And now Donald Trump might be poised to succeed that man as America’s oldest president ever.

After what happened with President Joe Biden, it’s no surprise that folks on the left have been speculating about Trump’s mental acuity every time he does something weird. Following last week’s town hall in Pennsylvania, I wondered if they didn’t have a point. After two attendees required medical attention, the former president jokingly asked whether anyone else wanted to faint, then abruptly stopped taking questions and converted the event into a literal listening session, asking for music to be played in lieu of the planned question-and-answer forum.

I won’t try to diagnose Trump’s mental state from afar (and for what it’s worth, at a subsequent town hall in Georgia, he seemed no more unhinged than usual). But regardless of whether Trump suffers from age-related cognitive decline now, there’s a high risk that sometime in the next four years, he will. Which is why we need a constitutional amendment to prevent someone so old from ever running for president again.

Even when you’re not doing the most stressful job in the world, age can be brutal on the brain. A 2022 study found that roughly one-third of Americans over age 65 have some form of cognitive impairment, and the older you get, the bigger the risk that your mind will start to go. Anyone who has cared for an aging parent or grandparent knows how suddenly that can happen: a stroke, a heart attack or an illness can impact a senior’s cognitive capacity, even if they don’t develop dementia.

The president is doing the most stressful job in the world, and that job has visibly aged every president in modern history. That toll seems likely to be heavier on older presidents - and if you doubt that, just watch Biden’s debate performance in 2020, then compare it with this summer’s performance. The president appeared a trifle slow four years ago, but it was nothing like the disastrous decline on display in June. When Biden visibly lost his train of thought and then helplessly muttered, “We finally beat Medicare,” I actually dove onto my couch in vicarious humiliation and covered my head with a pillow.

Trump won’t necessarily follow the same path if he’s reelected. But even a 5 or 10 percent chance that he might is unacceptable. In a nuclear-armed world where the fate of human civilization might hang on a president’s decisions, we can’t afford to have a commander in chief whose mind is no longer fully capable of rapid assessment and instant action.

Unfortunately, the 25th Amendment, which allows the vice president to temporarily assume power from an incapacitated president, offers no good way to remove a president who is lucid but no longer mentally sharp. It should function well enough in the situations for which it was designed, such as a president in a coma. However, if the president retains enough of his wits to contest the transfer of authority, we face a potential power struggle and a constitutional crisis.

That’s an argument for fixing the 25th Amendment. We should pass an amendment to screen out the candidates at the highest risk of such problems - which is to say, those in their 70s and 80s. Exactly what that age limit should be, and how to handle candidates who might exceed it in office, will need to be hashed out. I would set it at 72.

The obvious rejoinder is that passing a constitutional amendment is incredibly hard. But it’s not impossible. Nearly 8 in 10 voters support imposing an age limit on federal officials.

Those voters probably understand why it’s better to handle this through the amendment process than by expecting voters to provide a mental health check on the candidates. If a candidate does have cognitive problems, staffers and party insiders will try to hide that, as happened with Biden.

There’s also a political problem with leaving it to the voters. The structure of our electoral system strongly favors two major parties rather than many smaller ones. Americans can only really choose between two candidates, selected by a small group of primary voters.

Moreover, incumbents have so many advantages that it’s nearly impossible for primary voters to replace an incumbent, even when it’s clear that person has lost a step. Which is how we almost ended up having the third-oldest president in history face off against the oldest.

It’s too late to fix that problem for this election. If Trump wins, we must hope that if something happens, JD Vance can smoothly assume power before a crisis occurs. But we should act now to protect future Americans from the possibility of a president who cannot do the job and cannot be forced out of it, either.