It's also liberal propaganda concocted to convince voters that Trump is as feeble and demented as Biden; it has no basis in fact, and is a red herring meant to be a distraction from meaningful issues.
That said, here's two points to consider:
1. Trump's physical and mental condition allow him to still generate an excellent golf swing (at age 78), which requires strength, balance, mental concentration and hand-eye coordination. He recently played with Bryson DeChambeau in a pro-am match.
Physically, aging is a use-it-or-lose it endeavor when it comes to functional ability. What you don't use fades as we age. And even what we do use, generally declines. Trump is not immune from these effects. No one is.
Having eaten unhealthy food his entire life, and being opposed to exercise like he is (he has said so, and other than golf no one has seen him work out), and being overweight as he is, he seems to be blessed with good genes. Frankly, I'm surprised he has lived this long. To his credit, he does not drink or smoke.
His golf swing is weaker, not stronger, as would be expected in an aging male. That move has been well-rehearsed for decades and he continues to make it multiple times per week. Accordingly, his golf swing falls into the "use it" category.
Most of the time Trump spends on the golf course, he is seated in his golf cart. He carries nothing. People hand him his club. If he had to walk the distance from the tee to where his ball landed after a good drive, he would have a very difficult time if he could do it at all.
The use of some capabilities like a golf swing does not carry over to others. For example, having a good golf swing does not make it easier to walk up and down the steps of his airplane.
When you watch that, you'll see him moving slowly, firmly grasping the railing, and often looking at his feet. He still takes one step after another, but I expect to soon see him placing both feet on the same step before stepping up or down to the next.
Mentally, having a good golf swing does not keep him from slurring his words (anomic aphasia) and rambling incoherently at press conferences and rally podiums.
2. Trump went back to Butler, PA yesterday to a huge rally at the location of his first assassination attempt. Recalling that first event when he was shot, let's remember Trump's reactions during and immediately after shots were fired; he grabbed his ear and immediately ducked for cover before being smothered by SS agents. As he was being hustled off stage he had the presence of mind to stop and raise his fist in defiance, assuring the crowd he was OK. These aren't the actions and reactions of a feeble, demented and confused old man.
Even advanced Alzheimer's patients, have their moments of clarity. It is common for hospice patients to "rally" before death comes. They are unresponsive or barely responsive for a time. Then, a day or two or three before they die, they perk up and their loved ones notice the improvement. A good hospice staff will explain the rally to all concerned.
I'm not saying Trump is an advanced Alzheimer's patient or experiencing a hospice-type rally. I will suggest that getting shot has a way of getting your attention. The resulting adrenaline rush and intense focus explains his actions on stage that day. Trump did indeed have the presence of mind that day that you mention. That's the exception, not the rule.
Trump consistently navigates steps slowly, looking at his feet; slurs his words; rambles incoherently; often contradicts himself; and when he dances, it's nothing like he did before. He dances like one whose functional abilities have declined and continue to decline.