He was just 22 when he stood in the open turret of a 36-ton war machine as it rumbled down Route Irish outside the airport in Baghdad, peering through night vision goggles for possible targets on what was then the world’s deadliest highway.

Rock ’n’ roll blared through Jeremy Regnier’s headset on that October night in 2004. Then acrid smoke filled the Bradley Fighting Vehicle and the cocksure soldier from New Hampshire lay dead in the arms of a comrade, killed instantly by a crude roadside bomb.

Within hours — a half a world away — a black sedan carrying a military notification team crept slowly down a sloping driveway toward the Regnier home on a small hillside in Littleton.

And with that, the Regniers earned a designation no one wants: Gold Star family.

So when Kevin Regnier, Jeremy’s dad, heard Donald Trump belittle the parents of Captain Humayun Khan, a Muslim American soldier killed by a suicide bomber in Iraq, he was dumbfounded. When Regnier heard the billionaire assert that he, too, had sacrificed, his blood boiled.

“He compares himself to what we’ve gone through by attacking a family like that! But that’s Donald Trump,’’ Regnier said Tuesday. “He won’t back down. When someone attacks him for something he’s done wrong, he just does more wrong.’’

I first met Kevin Regnier 10 years ago, when I spent nearly a year with his family and his son’s military comrades of the First Cavalry Division for a series of Globe articles on post-traumatic stress disorder.

Like no other assignment, it profoundly underlined for me the steep price of freedom and the lingering, and sometimes, invisible wounds of war.

“Nobody should have to go through that,’’ Regnier told me. “And then for Trump to talk about his ‘sacrifice,’ well, that’s Donald Trump for you. He should just shut his mouth. He wants to be our commander in chief. Can you imagine what he’s going to say or what letters he’s going to write to families who lose a loved one in a war?’’

All this bluster from a man, who — The New York Times reports — was apparently “the picture of health’’ when he was 22 in 1968 and eligible for the draft as the war in Vietnam raged. And then this lucky diagnosis: bone spurs in his heels. Four other deferments, these for education, were to come his way.

And this guy dismisses a Gold Star family?

Rational political analysis would say that Trump has gone too far this time. Surely, he cannot survive this.

But I thought that last November when he cruelly mocked a Times reporter who has arthrogryposis, which limits the functioning of his joints. Trump’s performance then was juvenile and cringe-worthy and — I was certain — politically fatal.

I wasn’t alone. “No, this can’t be happening,’’ said Stan Eichner, litigation director of the Disability Law Center in Boston, recalling his reaction to Trump’s attack on Serge F. Kovaleski. “There must be some other explanation.’’

But there wasn’t. “The way he mocked him was just so troubling,’’ agreed Christine Griffin, the DLC’s executive director. “Everyone would say: That’s it. He’s gone too far this time. It shows the character of someone who shouldn’t be running for office, but there were a whole lot of people who didn’t care that he did that. And still don’t care.’’

We’ve seen Trump’s kind before.

Sixty-two years ago, a lawyer representing the US Army famously stood up to another demagogue, Senator Joseph McCarthy, during a hearing. Joseph Welch said this to McCarthy, effectively marking the beginning of the end for the dangerous Wisconsin Republican:

“Have you no sense of decency, sir, at long last? Have you left no sense of decency?’’

Wouldn’t that be a great opening question for this fall’s first presidential debate?

Mr. Trump, have you no sense of decency?

Thomas Farragher is a Globe columnist. He can be reached at thomas.farragher@globe.com.