Biden’s cognitive decline was on full, dangerous display at the presidential debate

President Biden speaks during Thursday's debate with former President Trump in Atlanta, Georgia. REUTERS

President Biden’s debate performance Thursday put his apparent cognitive decline on full and dangerous display.

For many months now, the 81-year-old Biden has appeared to be faltering and feeble when he ventures out in public.

Following the presidential debate, his wife Jill Biden had to lead him off the stage by his hand — a maneuver we’ve seen on several occasions recently, including an incident involving Barack Obama.

Biden often sounded indecisive as he spoke and was frequently unable to follow his own train of thought.

At one dramatic point he froze altogether after mixing up America’s supposed trillionaires (there are none) with billionaires, saying millions when he meant billions of dollars, claiming to have covered everyone’s health issues during COVID, and finally saying he had “beaten Medicare.”

“I really don’t know what he said at the end of that sentence,” Donald Trump adroitly responded to one meander.

“And I don’t think he did, either.”

It was a moment of pained levity, but presidential mental fitness is an extremely serious matter.

Back in July 2020, when I interviewed then-President Trump at the White House, he insisted that a president must be mentally “sharp.”

“Because I can tell you President Xi [Jinping of China] is sharp, [Russian] President [Vladimir] Putin is sharp, [Turkish President Recep] Erdogan is sharp,” he told me.

“You don’t have any non-sharp people that you’re dealing with.”

It was a key point lost in the internet explosion that followed when in the same interview Trump demonstrated his recall of the words “person, woman, man, camera, TV” as he described his own recent cognitive assessment.

Trump himself seemed quite sharp in that meeting, speaking without notes about questions he had not seen in advance — and, now 78, he continues to appear that way to me, although I haven’t since seen him in person.

But Biden’s performance is altogether different.

In February, Biden’s physician Dr. Kevin O’Connor tried to reassure the American public that the president’s comprehensive health exam, including a neurological assessment, was normal, and that Biden hadn’t suffered a stroke, Parkinson’s disease, or multiple sclerosis.

But the report lacked any kind of neuro-imaging (MRI) or cognitive assessment — a surprising gap, given Biden’s medical history.

Back in 1988 Biden suffered from an aneurysm of the brain that caused a bleed (subarachnoid hemorrhage).

The emergency condition required two open surgical repairs, using a now-outdated technique that can lead to long-term cognitive issues.

In addition, Biden has had an abnormal heart rhythm (atrial fibrillation) for many years, for which he takes a blood thinner — a medication that carries with it a risk of silent ischemia or silent strokes and long-term cognitive impairment, even dementia.

During the debate and in other appearances, Biden has appeared to exhibit physical unsteadiness and impaired balance — conditions that some neurologists have noted could be caused by Parkinson’s disease without a tremor or by normal pressure hydrocephalus, the buildup of fluid in the brain.

The president must undergo a thorough assessment for all these conditions, and related ones, in the wake of his debate disaster — and the American people deserve to know the results.

Of course, I have not examined President Biden.

But the symptoms I saw on Thursday and on many other occasions concern me, as they do millions of Americans.

And Thursday’s debate — itself a cognitive test in a sense, a stress test of neurological function — poured gasoline on the fire.

It’s absurd to blame Biden’s poor performance on a head cold, as the White House tried to do, or on cold medications he may have been taking.

A nasal or raspy voice was hardly the issue.

Even if a respiratory illness did play a role in making him more fatigued or forgetful during the debate, do the voters want a president who isn’t fully up to par because of a cold?

This isn’t a question of age: Cognition varies widely with age, and it isn’t fair to say that executive function is automatically impaired at a certain point in life.

But it’s a sad medical fact that a person with growing problems of memory and judgment is frequently the last to acknowledge it.

The debate exposed a weakness in the White House that has become impossible to ignore.

Marc Siegel, MD, is a clinical professor of medicine and medical director of Doctor Radio at NYU Langone Health and a Fox News medical analyst.