Khan is an immigrant and a Muslim. He came to the U.S. with his two-year-old son from the United Arab Emirates decades ago.
Years later, that son became Capt. Humayun Khan, an officer in the United States army. He was killed by a car bomb in 2004 while trying to protect the lives of his fellow soldiers.
At the Democratic convention, Khan the father, his wife at his elbow, reached out with a long, scolding finger to the unblinking eye of the television camera as though to single out Trump from the millions watching and speak directly to him.
"Donald Trump, you're asking Americans to trust you with our future. Let me ask you: Have you even read the United States Constitution?"
His voice was calm and steady, his sentences efficiently trimmed for maximum disgust.
"I will gladly lend you my copy."
A loud silence filled the arena.
He pulled a pocket edition of the U.S. Constitution from inside his jacket, raised it in his right hand and held it high.
Applause swelled. The audience rose.
"In this document, look for the words 'liberty' and 'equal protection of the law,'" he said.
And then came the shaming.
"Have you ever been to Arlington Cemetery?" Khan asked. "Go look at the graves of the brave patriots who died defending America. You will see all faiths, genders and ethnicities.
"You have sacrificed nothing and no one," Khan said, leaving us to remember the rest — he was a Muslim who had lost his son in the service of the country he'd chosen.
2 candidates, 2 narratives
It was for many the most moving moment of the convention — evidence there are Muslims who have embraced American values, defended American laws and died as American heroes.
It was high drama.
But did it make any difference; did it change anyone's mind?
A week earlier, Republicans had presented a different view of the impact of foreign-born people on American life and culture.
The device was the same — testimonials from those who had suffered sudden and tragic losses — but the examples involved crimes committed by illegal immigrants.
On the first night of the convention, three parents — Mary Ann Mendoza, Sabine Durban and Jamiel Shaw — told stories of how immigrants, in the country illegally, had killed their children. Two were drunk drivers involved in car accidents; another was a gang member who shot Jamiel Shaw Jr. in the head.
So much sorrow and sadness.
"Only Trump called me on the phone one day to see how I was doing," said Shaw's father.
Trump said nothing had affected him more than the time he had spent with "the mothers and fathers who have lost their children to violence spilling across our borders, which we can solve. We have to solve it."
And he repeated, for maybe the hundredth time or more, the facts behind the death of 32 year-old Katie Steinle: shot to death on a San Francisco pier in 2015 by an illegal immigrant who had already been deported from the U.S. five times before he was convicted for killing Steinle.
The testimonials — victim impact statements — were among the things that defined the differences between the two conventions: The dark and fearful view that America is broken and needs fixing — needs to be made "Great Again" — for which there is evidence.
And the sunnier view that America has always been great but, as its Constitution says, must be even greater and forever strive to be a more perfect union — for which there is also evidence.
Election day on Nov. 8 will sort out which view most people share.
But consider that Trump got a healthy five- or six-point bump in some polls after Cleveland. There are plenty who believe his dystopian analysis of America is the right one — he's "telling it like it is."
Democratic candidate Hillary Clinton will probably get such a bounce too a few days after the Philadelphia convention. If she doesn't, that probably spells trouble for her campaign.
In any case, this is what election 2016 has turned into: What matters most is not whether Clinton is "crooked" or whether Trump is a "fraud" — though those things do matter to many voters.
What matters is whether Americans believe their country is disintegrating.
The two party conventions argued irreconcilable answers to that question.
Most Americans will believe whichever one they want to believe.