Donald Trump committed probably his worst campaign offense so far last week, and given the other greatest hits in the Trump catalogue, that is an impressive feat indeed. What did Trump do? It definitely appeared to virtually every unbiased observer that Trump mocked a disabled reporter for his physical disability, which is the sort of thing that any halfway decent person, regardless of their political beliefs, would condemn.

The background of this story is set forth here, but stated briefly, Trump has found himself in a dispute with current New York Times reporter Serge Kovaleski about Kovaleski’s recollection of exactly how many Muslims were celebrating in the streets on 9/11. As it happens, there are two relevant facts about Serge Kovaleski that are important to this story – the first is that he suffers from a rare congenital condition called arthrogryposis which causes his arm to be bent over in a somewhat distinctive way. The second is that Kovaleski and Trump (from his time at the New York Daily news, when he covered Trump) have a lengthy and well documented history prior to this incident that appears to have been completely professional and friendly.

In the course of knocking Kovaleski’s failure to remember what Trump wanted him to remember (and which almost definitely did not happen), Trump performed an uncannily accurate caricature of Kovaleski’s disability, which you can see for yourself in the video below.

Now, Donald Trump does not explain himself. He does not look back. As an indication of how potentially damaging this story might be to Trump’s candidacy, Trump has twice now attempted to defend himself on the basis that he did not know what Kovaleski looks like, apparently alleging that he doesn’t recall Kovaleski’s condition and thus couldn’t have been mocking it.

I do not know the reporter for the @nytimes, or what he looks like. I was showing a person groveling to take back a statement made long ago!

— Donald J. Trump (@realDonaldTrump) November 26, 2015

The reporter who pulled-back from his 14 year old never retracted story is having fun. I don’t know what he looks like and don’t know him!

— Donald J. Trump (@realDonaldTrump) November 28, 2015

Trump has now taken his denial show one step farther, insisting that not only does he not owe Kovaleski an apology, the New York Times owes him an apology for… I’m not sure, exactly. Hiring a disabled reporter and baiting him into the trap of mocking said disabled reporter.

There are a couple of major, major problems with the idea that Trump did not know what Kovaleski looked like and was not mocking his disability and I set those forth over the weekend. However, the biggest problem of all is Trump’s own words in the video about the man he apparently has never seen or doesn’t remember ever having seen.

What does he say about him, specifically, before he goes into his very visual mockery of Kovaleski?

He says, “Now, the poor guy, You gotta see this guy…”

Whereupon, he immediately stuck his arm up, cocked his wrist just like Kovaleski’s, and did a junior high bully’s best impersonation of a person with mental disabilities.

“You gotta SEE this guy, Donald?” Why would you possibly have said that immediately prior to launching into a perfect visual representation of his disability, if you yourself didn’t know what he looked like? “You gotta see this guy,” right before you do an impersonation, is not something you say about a person you yourself have not seen. Especially when preceded by “the poor guy,” which is pretty good proof that he knew specifically that the reason Kovaleski looks that way is that he was disabled.

Judging by the angry reaction from Trump supporters I got all weekend on Twitter for covering this story, most Trump supporters (at least the ones on Twitter) are perfectly happy being despicable people who actually cheered Trump’s mockery of Kovaleski’s condition. And so, people say, “why bother? Nothing you say will cause Trump’s supporters to leave him at this point.”

Probably true. But right now, 75% of the GOP electorate is supporting someone other than Trump. When those candidates inevitably drop out one by one, inevitably their supporters will be looking for somewhere to go. It is important, for the sake of the party and thus the country, that that 75% does not find Trump an acceptable option at all.

Nothing either will or should drive that point home than the realization that one of the richest and most powerful men in the world has no problem mocking the disabled for their disabilities.