Just like the man they stand behind, backers of President Biden can be a feisty bunch.

Even as more prominent supporters jump ship — Hollywood high rollers George Clooney and Rob Reiner say it’s time for Biden to step aside, and former House Speaker Nancy Pelosi stopped short of saying she wants Biden to stay in the race — true Bidenistas are digging in.

There’s California Gov. Gavin Newsom, of course, and various House and Senate members who believe Biden should stay the course. But I’m hearing directly from readers ticked off about my column suggesting that Biden undergo a full battery of neurological testing (based on assessments by doctors I spoke to) to reassure the public that he’s OK, as he defiantly insists.

“You should get tested and the results be made public,” said Dan Cordova of Albuquerque. “You should also retire and go back under a rock.”

“SHAME ON YOU for adding to the Biden media feeding frenzy,” wrote Marcy Rothenberg of Porter Ranch. “It’s already been reported that President Biden has arthritis; his back is stiff so he walks slowly. He still can ride a bike. Can Donald? No. He can’t even walk a golf course.”

Even former state legislator and L.A. County Supervisor Sheila Kuehl shook a stick at me.

“Instead of joining an echo-journalism ignorant drumbeat, perhaps you might have, as [history professor and essayist] Heather Cox Richardson did, revealed the letter from the President’s actual doctor, Dr. [Kevin] O’Connor, on his neurological exam at the end of February. I hope you will read her as thousands do every day and reveal this in a column.”

I understand and respect Biden loyalty. As I’ve said before, he seems to be a decent and civil man and he’s been a good president.

I also believe, and have often stated, that former President Trump is a menace, and I don’t know who the greater threat to the republic is — him, or all the lemmings in line to hand a second term to a lying, hateful, vindictive, narcissistic felon who failed to deliver on virtually all of his campaign promises (look it up if you don’t believe me).

Readers have asked how I could write a column saying Biden should undergo testing, but not Trump, who has had his own particular set of behavioral issues. I assumed it went without saying that Trump ought to have his head examined. But sure, I’ll get on board with both of them getting a full diagnostic workup.

I loved the suggestion by Terry Spencer of Highland Park that Biden and Trump should have to take the intentionally confusing California DMV license renewal test, and whoever scores highest wins the election.

The Biden backers seems to fall into one or more of three categories. Those who think his health is good enough to handle the job going forward. Those who think it’s too late to switch to a replacement candidate. And those who would vote for a bean and cheese burrito before they vote for Trump.

“I never give much credence to polls, but Biden still does better against Trump than others,” said Kuehl, who added that the chaos of “changing horses in midstream” would do more damage to the party “than sticking with Joe, who, I think, will win.”

Plausible, but the stream is deep, and the horse’s head is barely above water.

A reader named Mark Richardson, of Encinitas, is banking on a passing of the torch, but not just yet.

“We’ll see how the next couple of months go, and if he gets elected, he can resign a month after inauguration day, January 2025 and [Vice President Kamala] Harris can take over,” Richardson said.

Also plausible, but the key words are “if he gets elected.” I have serious doubts, and said earlier this month that Biden should pass the baton and walk away with pride, dignity and grace. Not because of his age (lots of older people are fully functioning), but because of his health.

The president didn’t improve his chances with his stiff gait, slack expressions and word stumbles in the June 27 debate. His judgment wasn’t sharp, either. Instead of getting lured into a silly back-and-forth about which candidate is the best golfer, Biden should have said that as the planet melts and women’s reproductive rights have been stolen by Trump’s Supreme Court, he’d rather talk about saving the country than playing golf.

Things did not get much better for Biden in the televised ABC interview a few days later. And as for the doctor’s report cited by Kuehl and countless others, based on a physical Biden had in February, it leaves a lot of questions unanswered.

“An extremely detailed neurologic exam was again reassuring in that there were no findings which would be consistent with any cerebellar or other central neurological disorder, such as stroke, multiple sclerosis, Parkinson’s or ascending lateral sclerosis, nor are there any signs of cervical myelopathy,” said the report from Biden’s doctor.

I’m not taking any statement from the White House as gospel truth, regardless of who’s in office, and I have questions.

When exactly was the neurologic exam taken and by whom? What is meant by “extremely detailed?” And given the progressive nature of memory and movement disorders, isn’t it possible Biden’s condition has changed in the last six months, and will continue to do so?

As Kuehl noted, there’s a big difference between the opinions of physicians making a diagnosis from a distance and those who actually see the patient in question. I couldn’t agree more, and in fact, I wrote a column chastising people who thought they could diagnose dementia in Biden by watching him on CNN. Dementia is not some catch-all phrase for a memory lapse, which could be caused by any number of things.

But no matter how much you love Biden, hate Trump, or both, I don’t know how anyone could have watched that debate and not be worried about Biden’s health.

Neurological movement disorders are often accompanied by specific symptoms that doctors can spot. Several reached out to me after the debate to say they saw signs of Parkinson’s or a related condition. Two neurologists took note of Biden’s blink rate, facial expressions, stiffness and speech patterns.

One, Dr. Michael Mahler, a neurology specialist and UCLA faculty member, said he suspected something in the “Parkinsonian” paradigm.

Dr. Jack Florin, who has been a USC professor and had research fellowships at Stanford and Harvard, said he thinks Biden suffers from a Parkinson’s variant called progressive supranuclear palsy (PSP), which can involve cognitive impairment that worsens over time and impact mental processing speed, attention and concentration.

The White House report on Biden’s health didn’t convince Mahler or Florin that we know the full story, or that their own impressions of Biden’s condition are off base. Florin suggested that an MRI, if there hasn’t already been one, would be helpful in supporting his theory that Biden has PSP.

Mahler said “some of the disorders in the realm of Parkinsonism are inherently variable,” meaning that they change over time. And “having a normal neurological exam in February (or earlier) means nothing if a person had a stroke or series of small strokes in March.” But he was cautious about making a specific diagnosis, and said medication for certain disorders can produce symptoms that mimic Parkinson’s.

“One thing that Biden has repeated is that functioning as president is a harder test than asking him to draw a clock or recall five words, and that is probably true,” Mahler said. “Yet it is also true that neurologists around the country saw something during the debate other than reassurance that the president was neurologically fit.”

What I saw was a sad moment in U.S. political history.

A tyrant counting on victory in November.

A weakened president trying to stand tall.

Some of his supporters abandoning him and others doubling down.

It may be that neither candidate gets tested, but come November, all of us are going to be.

steve.lopez@latimes.com