The battle between the Khan family and Donald Trump may be the straw that finally breaks the camel’s back of the Trump quest for the presidency.

You know the background, and this weekend the level was elevated when Mr. Trump cranked it up by suggesting that Mrs. Khan, who did not speak during her husband’s time on stage at the DNC, was being silenced because she was a Muslim woman and they’re not allowed to speak.  (Mrs. Khan responded here.)  He justified his further attacks on them as payback for their “vicious” attack.

The response to Mr. Trump from every corner has been loud and harsh, not seen on this level since he attacked the judge overseeing the civil suit against “Trump University” as being biased because of his Mexican heritage, and his criticism of a family who lost a loved one in battle reminded people both of Mr. Trump’s lack of military service and his attack on John McCain for having been held as a POW in Vietnam.

In any other presidential campaign, such an incident would have doomed the candidacy, but as we’ve seen time and again, Mr. Trump not only survived them, he actually got a bump in some polls.  As he once noted, he could kill someone on 5th Avenue in New York and still get votes.  So is there any reason to think that this particular battle will cause him any harm?

But even in this campaign’s environment of no-holds-barred attacks and counterattacks, there are certain lines you do not cross.  One of them has been going after those who died in battle and their families.  Anyone with any sense of decency would know that.  But it seems that Mr. Trump is lacking in that department and so, in the words of Joseph N. Welch spoken to Sen. Joseph McCarthy in 1954, we have to ask, “Have you no sense of decency sir, at long last? Have you left no sense of decency?”

I don’t know if this incident will do it.  There have been so many other outrages that should have relegated Mr. Trump to the ash heap of history and yet he still survives.  But if there is an ounce of decency and self-respect left in the American electorate who support him, this may be, at long last, the outrage that ends it.