I absolutely acknowledge that many, if not the majority of people with ADHD, have at least one more condition.

But we can be certain Trump meets criteria for ADHD, whereas more assumptions are involved (we need to know motivation for behavior) for a Narcissistic Personality Disorder diagnosis.

Furthermore, some of the behavior (like hyperactivity, described in this article) has nothing to do with narcissism. And even Trump's narcissism doesn't make much sense without understanding his ADHD - why would someone who has told us he wants to be seen as a stable genius keep blurting out comments that are so clearly incorrect and make him appear ill informed?