President Biden’s mental acuity, which has shown signs of fading that is weakening his re-election bid, faces the most crucial test of all on Thursday when he steps on the debate stage in Atlanta with former President Donald Trump.

Episodes of freezing up or wandering away and sentences trailing off in gibberish have characterized several of Mr. Biden’s recent public appearances, especially those that do not allow the 81-year-old to rely on a teleprompter or support from a team of aides.

Mr. Biden won’t have any help on stage at CNN headquarters, where he’ll face 90 minutes of questioning while standing up, with only a pen, paper, and bottle of water allowed on the podium. Written notes are prohibited as are consultations with aides during the two commercial breaks.

In other words, Mr. Biden, who is accompanied by a half-dozen staffers just to walk across the White House lawn, will be unassisted during one of the most important events of his political career and as public confidence in his fitness for office has plummeted.

“This will be the most strenuous test of his mental fitness at a time when he has been showing an accelerated decline,” said Dr. Carole Lieberman, a forensic psychiatrist based in Beverly Hills, California.

Mr. Biden’s critics and health professionals, including Dr. Lieberman, believe that to avoid a disaster Thursday night, Mr. Biden will need performance-boosting drugs, which some claim, without evidence, he used to deliver an energetic State of the Union address to Congress in March.

Mr. Trump this week called for both of them to take a drug test ahead of the debate, a call echoed by several other Republicans, including Rep. Ronny Jackson of Texas. Mr. Jackson, a former White House physician, on Tuesday demanded a pre-debate drug test for Mr. Biden, who he has regularly accused of suffering from signs of dementia.

“If President Biden needs to take performance-enhancing drugs in order to participate in this week’s debate, then it is imperative that he and his physician disclose that to the American people,” Mr. Jackson wrote to both Mr. Biden and White House physician Kevin O’Connor.

Mr. Jackson suggested the president might be administered a drug called Provigil to increase alertness. The drug, approved by the FDA in 2004 to treat narcolepsy and other sleep disorders, is nicknamed “Viagra for the brain.”

But such drugs, and others such as Adderall, a treatment for attention deficit hyperactivity disorder, can only help Mr. Biden to a small degree, neurologists say.

One prominent neurosurgeon who requested anonymity said Adderall or Provigil would aid in making Mr. Biden appear more alert but would do little to enhance the president’s cognition.  

Given Mr. Biden’s recent public displays of mental frailty, the doctor said, “It’s very challenging to see a reliable cognitive functioning performance without a teleprompter.”

With his reelection on the line, Mr. Biden and his team of aides dropped everything this week to help the president prepare for the debate, leaving Washington for the isolation of Camp David in Maryland’s Catoctin Mountains.

There, according to reports, at least 16 staffers have gathered to help him prepare for the debate and have outfitted a mock debate stage complete with lights and production equipment.

The debate will give Mr. Biden the best opportunity to show wary voters he is fit for a second term following numerous polls that show a majority, including critical independents, believe he is too old for the office.

Ratings are likely to be significant. The sole 2020 debate between Mr. Trump and Mr. Biden attracted 73.1 million viewers, according to Nielsen.

Overall, Mr. Biden is trailing Mr. Trump slightly in most national and battleground state polls.

Mr. Trump’s critics say the former president and his team are now trying to increase expectations for Mr. Biden ahead of the debate, which many believe is set up to favor Mr. Biden over Mr. Trump.

The CNN moderators each have displayed public bias against Mr. Trump and the rules allow them to cut off mics, which will prevent Mr. Trump from interrupting Mr. Biden with memorable one-liners. There will be no live audience to root for the former president, who is fueled by energetic crowds.

“If Biden has a good debate on Thursday night, performance-enhancing drugs may be the Trump campaign’s excuse,” pollster Frank Luntz predicted on X.

• Susan Ferrechio can be reached at sferrechio@washingtontimes.com.