An alarming result, but we can all be thankful this holiday season that there’s a highly competent, highly regarded vice president waiting in the wings in case Biden can’t do his job anymore.

I’ll repeat what I said a few weeks ago, the last time we got some data showing Americans taking a dim view of the president’s mental acuity. Politicians can always hope for a turnaround on basic polling metrics, like job approval, based on events. Inflation might ease, the supply chain might stabilize, the economy might improve. But people typically don’t change their minds about an elderly person’s mental capacity once they’ve formed a suspicion that that person has lost a step. Senescence proceeds in only one direction. If you’ve become convinced that Sleepy Joe really is sleepy, it’s unlikely that there’s anything he can say or do that’ll change your mind. At best, if he seems energetic and cogent at this time next year, you’ll conclude that he hasn’t gotten any worse.

There are a lot of voters out there who question Biden’s fitness for the job and the number is growing, which compounds the Democratic dilemma in 2024. Even if he’s willing to run again and has a high enough approval rating to give him a fighting chance at reelection, do they dare stick with an 82-year-old whom huge numbers of Americans already believe is fading?

Only 40 percent of voters surveyed agreed with the statement that Biden “is in good health,” while 50 percent disagreed. That 10-percentage-point gap — outside the poll’s margin of error — represents a massive 29-point shift since October 2020, when Morning Consult last surveyed the question and found voters believed Biden was in good health by a 19-point margin.

Asked whether Biden is mentally fit, voters are almost evenly split, with 46 percent saying he is and 48 percent disagreeing. But that negative 2-point margin stands in stark contrast to Biden’s numbers last October, when voters believed he was mentally fit by a 21-point margin…

A recent Harvard-Harris poll found that 53 percent of voters said they had doubts about Biden’s fitness and 47 percent did not. Asked if Biden is too old to be president, 58 percent said he was and 42 percent said he was fit enough.

How does Biden grow his job approval if the public doubts his mental fitness and is unlikely to have those doubts eased over time? If you believe he isn’t competent in the psychological sense of that word, how can you believe that he’s competent in the professional sense? You don’t often hear it said of a senior citizen, “He’s senile but damned good at his job.” Especially when it’s the most important job in the world.

This is why I wonder whether there’s a de facto ceiling on Biden’s approval rating. The more people become convinced that he’s unfit, the less likely they are to credit him with a job well done. Is it a coincidence that his numbers on virtually every conceivable positive metric have fallen over the past six months, not just health and fitness?

Since May, fewer voters see President Biden as compassionate, capable or caring about them. https://t.co/Opfuf1XHcP pic.twitter.com/3rbw2JPDOt

— Morning Consult (@MorningConsult) November 17, 2021

The only hopeful spin available here to Dems is that perceptions of Biden’s mental competence aren’t driving perceptions of his professional competence. Rather, it’s vice versa. Because the public has soured on him due to Afghanistan and inflation and the resurgence of COVID, they’re more likely to view him as not mentally up to the job. Morning Consult’s data provides some support for that theory, as the share that rates Biden as mentally fit is higher than the share that rates him as capable of leading the country. On mental fitness the country splits 46/48, with independents at 42/47 and suburbanites at 46/46. On his capability to lead the U.S., voters split 41/53. Independents are at 36/53(!) and suburbanites at 43/51.

So maybe I’m wrong in this case about the electorate’s opinion of Biden’s mental acuity being doomed to decline over time. If they’re treating that assessment as just another proxy for how good he is at his job then an economic rebound and the eventual decline of COVID might convince voters that he’s on the ball after all. His job approval will rise and the sense that he’s mentally fit will rise with it. Democrats had better hope so, because at the moment they’re staring at a 2024 rematch with Trump with nothing but weak politicians as potential nominees. Joe Biden in an even more advanced state of decline might realistically be their strongest hand.