TL;DR: if you care about anyone disabled, then vote, and vote for Hillary.
I'm privileged that for 40 years I was able. Walking wasn't hard, conscious work, reading wasn't a difficult chore and balance was not a foreign concept to my body. I like to hope that I was a decent compassionate person and treated disabled people as full human beings with dignity and respect, but I can't be certain that - in my ignorance - I didn't slip up. I see unheeded mistakes and forgive them silently often enough.
Now, I'm doubly privileged to live with disabilities. Sure, they're a wretched pain in the neck, and nearly five years after my strokes I no longer remember what it was like not to struggle with simple things. Intellectually I know that I ran and jumped, read voraciously and could easily stand on one leg, but I can't imagine how. I say that I'm privileged to be disabled, because it's not that bad for me. It's terrible, but I've met people who have it worse, and now I know how lucky I was, without even realising.
It has made me pay more attention to how disabilities are portrayed and represented, and conscious of things that never registered before, and I'm glad because how we, as a society, show and interact with any minority speaks about what kind of society we live in. As with society as a whole, how individuals behave matters, especially when they are nominated for the US presidency.
Alone, I would consider that unacceptable. Even as a joke it's not OK, and there is no evidence that Trump was joking, nor that he can joke. He says what he means and he means what he says.
It's worse though because it reveals a horrible facet of Trump: he mocks because he thinks less of the other person, not for his ideas but simply because the reporter is disabled. He thinks that it is the norm to discount someone because they're disabled and is comfortable doing so.
Just to be clear: Donald J Trump thinks less of a disabled person because they are disabled.
If it was just disability, I would not be as ardent an advocate for ensuring he never gains the Presidency, but it's not, and he has shown that:
Trump thinks less of women.
Trump thinks less of people of colour.
Trump thinks less of LGBTQ+ people.
Trump thinks less of Muslims.
Trump thinks less of refugees.
Trump thinks less of immigrants.
Trump thinks less of PoWs.
All of those things disqualify him, and in sum, make him the antithesis of an American President. The President both represents and defines American society. In allowing Trump to become President, you would be acceding to his view of humanity and shaping US society; you are saying that you are OK with a worldview that sees the able as inherently superior to the disabled, men superior to women, whites superior to others, straight inherently superior to gay, and so on.
I think that is worth voting against. I'm sad that the US presidential race is still binary, but realistically, the only way to vote on November 8th is for Hillary Clinton, and you must vote.