The question isn’t whether Trump or Biden is declining faster: it’s why the US is faced with this choice | Emma Brockes

No election involving Donald Trump can be considered normal, but, in among all the breaches and oddities of this uniquely strange presidential race, one stands out as stranger than others. That is: speculation as to which of the two presidential candidates is showing the greater and more alarming rate of mental decline.

Until recently, this topic was considered at best unsporting, at worst dangerous – particularly on the left, where it is assumed that discussions around age will hurt Biden more than Trump. Even Trump, however, has benefited from certain delicacies governing the subject of impairment. During his first run for president, when the words “narcissist” and “borderline personality” first started to be bandied about, plenty of mental health professionals popped up to steeple their fingers and point out it is neither polite nor judicious to diagnose others based on zero clinical information.

Since then, all standards have lowered, cognitive impairment has become a major part of Trump’s campaign to undermine Biden, and both men – 78 and 81 respectively – have behaved in ways that might give even the most cautious observer pause.

These are two of the oldest people ever to run for president , at a time of unprecedented video documentation and manipulation, and in a race in which the stakes are so high you would have to be superhuman not to suffer the occasional lapse. Meanwhile, both are folksy, unorthodox communicators, with none of Obama-the-lawyer’s facility for pitch-perfect off-the-cuff eloquence.

Still, the evidence of decline on both sides is compelling. Let’s start with Trump. There is something grimly amusing about the defence that he has always been like this: hopelessly inarticulate, hopping between subjects on the winds of his own energy and inability to listen. For a long time, it worked. Over the last few years, however, Trump’s verbal style has loosened into something more incoherent than charming. At a rally in Virginia earlier this year, he remarked : “Putin has so little respect for Obama that he’s starting to throw around the nuclear word,” not the first time he has confused Biden with Obama.

He has struggled to pronounce a variety of words, including “ Venezuela ” and “ respected .” And his verbal range appears to have narrowed. As far back as 2017, Martin Amis, a closer studier of language than most, observed to me in an interview: “If you look at old tapes of him on [US talkshow] Charlie Rose, [he was] using words like ‘chagrin’ correctly. And with a certain amount of ironic reserve.” (This is true. Go back to footage of Trump from 1992, and while the verbal tics are all there – his reliance on words like “tremendous” and “horrible” – the fact is, he is much more fluent.)

Biden has made similar errors. The transcript of a recent interview with Time magazine was brutal. The president had to double back to correct himself after mistaking Iran for Iraq; appeared to jump, while talking about the environment, between the Amazon and Angola with no connective thought in between; and twice corrected himself after suggesting Putin had invaded Russia, not Ukraine. In a discussion about the security threat posed by China, the transcript includes the devastating parenthesis, “[Editor’s note: Biden appeared to mean Xi here, not Putin.]”

And the visuals don’t help. By tacit agreement, there seems to be a well-meant reluctance to publicly point out something that privately everyone is saying: who did Biden’s face?! Why didn’t he call Meryl Streep, who at 74 is ageing better than anyone in Hollywood, and thus the world, to ask for a recommendation? His skin is sheeny, and somehow both puffy and taut, and the result is incredibly ageing – as, I might add, is Trump’s weight loss, which has made his face go the full Edvard Munch .

Within these discussions there is still, on both sides, a lot of grabbing at straws. Trump recently mixed up Sioux City and Sioux Falls at a campaign stop in Iowa, which seems to me entirely understandable. And the heavily touted videos of Biden “wandering off”, first at the G7 in Italy, then at a fundraiser in LA, appeared questionable. On closer inspection , it seemed that the New York Post, in sharing the G7 video, had cropped it to make it look as if Biden was wandering into an empty field rather than addressing a paratrooper off to one side. Still, he walked slowly and hesitantly in a way that hurt my heart, which is definitely not ideal in the context. You don’t want to look at a candidate for president and have the first thought out the gate be: “Poor guy.”

And so, while we can reassure ourselves with the reminder that, for example, George W Bush said things such as: “Families is where our nation finds hope, where wings take dream,” and he was only in his 50s, the more depressing fact about all of this is that out of a population of more than 330 million, this is the choice we face. You can be old, infirm, not on top of the details and hopelessly inarticulate, or at least give a very strong impression that all of these things are true. But as long as you are a white man, you can still be president of the United States.

• Emma Brockes is a Guardian columnist