So I've been reading his book, and monitoring his behavior, and as someone with a high-functioning autistic sibling, I think Donnie might have something undiagnosed.

Let's look at how he behaves (most of this is common knowledge, so I won't use sources).

1.) he doesn't shake hands/touch people.

It's a known fact that many autistic people dislike being touched, especially by strangers. It's possible his germophobia either exacerbates this or is an excuse for him not wanting to be touched.

2.) Very little subtext in his speech

Many autistic kids say directly what they mean, don't use/overuse conventions like sarcasm or subtlety, and often eschew nonverbal communication for verbal. Donald does this a lot. He always says directly what he thinks, even if it's unflattering/unpopular/offensive.

3.) Lack of social filter/impulsive behavior

Do I have to explain this one?

4.) intense focus on a select few things

In his book The Art of the Deal, he expresses that he hates small talk, doesn't like to discuss personal issues, and generally finds parties/ceremony to be tedious and obnoxious. He writes in broad strokes except when he's talking about business. Then it can be very hard to keep up, with him using many technical terms, going into unnecessary detail, and consistently talking about how much he loves making deals.

5.) verbal tics

He kept sniffing again and again during the first debate. I know this one is a stretch, but I'm including it anyway.

6.) Problems paying attention

During intelligence briefings, debate prep, and general consultation, many report that Donald cannot focus, that he looks out the window, and just generally distracts himself.

7.) repetitive behavior

He loves routine. He won't leave his homes, he intended to carry on his pre-president lifestyle even after he got to the white house, and in his book he says his routine is almost always the same.

8.) sleep dysfunction

He's always tweeting at 3am, so obviously he has an irregular sleep schedule. I know this is reaching, but it lines up.

So there you have it. Doesn't excuse his behavior. But it might explain a lot of it.