I saw the full speech start to finish, I don't buy it at all personally that he wasn't doing a disabled mock.
If you are mocking a disabled person, I don't imagine anybody thinks "Hangon, best mock this disabled persons exact condition in a physically and scientifically correct way", you just go with the generic disabled person look which it seems very much like what he did. We will never know if that's what he actually intended, but myself watching the video personally, it seems like he is very much mocking a disabled person.
Either way, that part is pretty irrelevant. It's highly unprofessional to mock anyone, for any reason, in public. You'd get disciplined in a lot of workplaces for doing it, let alone as president of the United States in front of hundreds of millions of people.
I mean for entertainment purposes, it's excellent. But it shows a serious childish lack of restraint. We all joke and mock and make fun of friends or people for a laugh in a private audience, and I wouldn't expect the president to be any different. But there is a time and place, and that wasn't one of them.