Thank you Karen, for your thoughtful analysis of Trump's speech patterns.
Much of what you describe, particularly the stream of consciousness, and an inability to stay on track with any one idea, fits well with an ADHD diagnosis. I have written extensively about this on Medium,
https://dockruse.medium.com/can-we-talk-about-donald-trumps-adhd-now-764ec019db82
and devoted most of a book to this.
While it would be unethical to betray a patient's confidential information without their consent, a diagnosis of ADHD can be made from the extensive public record because the definition for ADHD is written entirely in terms of observable behaviors. And objectively, Trump has displayed more than enough symptoms to qualify.
The increase in the severity of Mr. Trump's ADHD symptoms over the last few years could be signs of significant stress, a combination of ADHD and "normal" aging, or might be indicating a form of dementia along with the ADHD. But all of these are speculations, whereas the ADHD diagnosis is grounded in observable facts fulfilling a validated set of diagnostic criteria.