I can’t imagine why.

NEW – Biden falls asleep at #COP26 "climate change" conference. pic.twitter.com/Y5hR7CCghn

— Disclose.tv (@disclosetv) November 1, 2021

Before you throw stones at him over that clip, ask yourself: Could you stay awake during a conference on climate change? At any age?

Most presidents who see their polls slide can tell themselves plausibly that things will turn around. They’ll pass a major bill; they’ll have some sort of diplomatic victory abroad. Obama crawled along in the mid-40s in job approval for much of his presidency but surged at the end. Biden could tell himself the same story, that he’s one infrastructure deal away from a renaissance.

Heck, he might not even need infrastructure for his numbers to rebound. If America gets through the winter without being brutalized by COVID the way it was last year, voters may conclude that we really have turned the corner on the pandemic. Optimism will return. People will begin to believe again that the country’s on the right track.

But maybe there’s a complicating factor in Biden’s case. Not since Reagan have we had a president whose mental acuity due to age was in serious doubt. Trump has been dissected psychologically a thousand different ways but “senile” usually isn’t part of the diagnosis. I wonder if Biden’s struggles this past summer, starting with Afghanistan and bleeding over into COVID’s resurgence and the infrastructure standoff, convinced Americans that he’s simply not up to the job. And by “not up to the job,” I don’t (just) mean “not good at the job.” I mean too enfeebled mentally due to age to ever do it effectively.

If that perception has set in, I wonder if there’s anything that could reverse it, realistically. Even if COVID recedes and the economy starts humming, maybe the way swing voters view Biden as a person has now iced over and there’s simply no way to convince them that he’s fit for duty. He’s getting older every day, after all. If I’m right then he’ll never see a durable rebound in approval. He may catch a bounce every now and again based on good news, but a sustained resurgence? Nuh uh.

How can you convince yourself that someone’s doing a good job after you’ve concluded they’re not mentally sharp enough to hold that job in the first place?

That’s not an outlier. Last month Pew found 43 percent of Americans willing to say that Biden is mentally sharp, down from 54 percent earlier this year. Coincidentally or not (probably not), 42-43 percent is right around where his job approval is.

If I’m right that Biden’s approval is bound up in perceptions of his basic fitness to a greater degree than it is for other presidents then his downturn in polling may be “stickier” than downturns other presidents have experienced. The counterargument would be that the opposite is true, that it’s not perceptions of his fitness that are driving his job approval but vice versa. Once he starts having some political success again such that voters approve of his performance, they’ll reason themselves into believing that he’s fitter than they thought.

On a gut level that strikes me as unlikely, though. How often have you watched an elderly person for a long period of time, arrived at the belief that they’ve lost a step, and then had to revise that opinion because they went on to impress you somehow with their sharpness? Normally when you conclude that grandma or grandpa is slowing down, you never again sense that they’re speeding up. Age doesn’t work that way.

The killer for Biden in this poll is that opinions about his mental sharpness are conspicuously weak among some groups he’s counting on in 2022 and 2024. Just 34 percent of independents see him as sharp and only 40 percent of women, a key Democratic constituency, do. The group that delivered the presidency to Biden last year, suburbanites, split 43/51 on his mental sharpness. As much as suburban voters might hate Trump, do we expect 82-year-old Joe Biden to draw the same level of support among them in 2024 if only 40 percent or so deem him cognitively capable of doing the job?

Swing-district Dems are ruminating on that today and mulling over this new poll from Morning Consult and feeling sweaty:

Some of the largest drops in Biden’s suburban support came in 2022 battlegrounds:

Wisconsin: -11
Florida: -11
Ohio: -10
North Carolina: -8
Georgia: -4
Michigan: -3
Pennsylvania: -3
*Net approvalhttps://t.co/JQLyxhvuEG pic.twitter.com/17g7XT2mqF

— Morning Consult (@MorningConsult) November 1, 2021

Being net negative in the suburban Rust Belt is a dangerous place for Joe Biden and his party to be after only narrowly winning those states last fall.

The poor ratings on his mental sharpness may help account for the result in the other splashy poll circulating today, the fact that a plurality of Dems want a different nominee in 2024. If you’re faced with a choice between an 82-year-old who’s already begun to decline and literally anyone else, “anyone else” is an attractive option. But tell me who. Kamala Harris? C’mon. Pete Buttigieg, who struggled throughout the 2020 primaries to attract any black voters? Please. Stacey Abrams, who’s never even held statewide office?

They have no bench, no star waiting in the wings with the retail chops and the experience to be a plausible winner in a national election. And Jonathan Last may be right that there’s no other Democrat capable of holding together Biden’s coalition of nonwhites and well-educated whites. Even Biden himself may not be capable any longer of holding it together given his deterioration among suburbanites. But then, the “Biden coalition” might not be a true Biden coalition; it might simply be an anti-Trump coalition. Whether that coalition would reassemble when faced with a choice between Trump 2.0 and reelecting an already sundowning octogenarian, I don’t know. The GOP could avert that suspense by simply nominating someone else but it’s not like Republican voters nowadays to do the obviously right thing. Stay tuned.