[throwawaydad12]

> there’s a video of him doing just that

I believed that for years. It just sounds like the sort of oafish, lame humor I'd expect from him.

But finally, I looked more deeply into it. My impression from that dive is that he was not specifically mocking this reporter's disability. Rather, it's more of a theatrical way of saying "Duh!", which he has used on many prior occasions, and even occasionally when referring to himself. (And of course, "duh" comes from a meaning of mocking people with low IQs or other similar disabilities. You could argue that it's wrong, but it's not particularly unusual in American discourse.)

It's somewhat open to interpretation, but I think a reasonable person could come down either way.