Mark S. Byrnes is professor of history at Wofford College in Spartanburg, SC.

Donald Trump’s style, as many observers have noted, has much in common with the demagogue of the early 1950s, Sen. Joseph McCarthy. The New York Times has noted that McCarthy’s henchman Roy Cohn was a kind of mentor to Trump. In my last piece, I noted that the Republican Party establishment then, as today, tolerated both only to find to their dismay that reckless demagogues cannot be controlled.

Many people—myself included—have expected Donald Trump to self-destruct in this campaign. We thought he did so even during his announcement speech, with its openly racist denunciation of Mexicans. We were certain it was going to happened when he denigrated Sen. John McCain and callously said “I like people that weren’t captured.” There have been countless other examples over the last year, none of which has brought him down.

It’s important to remember that McCarthy was not brought down by what he said, but by what others had to say about him. Edward R. Murrow used his program “See It Now” to expose McCarthy.

Most famously, in the so-called Army-McCarthy hearings,* Army attorney Joseph Welch called out McCarthy on live television, when McCarthy tried to smear a young lawyer on Welch’s staff. Welch memorably replied:

“You’ve done enough. Have you no sense of decency, sir? At long last, have you left no sense of decency?”

In that moment, most decent people realized the answer to that question was “no,” and McCarthy was spent as a political force.

On Thursday night, Khizr Khan, whose son was killed in action in Iraq, asked Trump:

“Have you even read the United States Constitution? I will gladly lend you my copy. In this document, look for the words 'liberty' and 'equal protection of law.'

Have you ever been to Arlington Cemetery? Go look at the graves of brave patriots who died defending the United States of America.

You will see all faiths, genders and ethnicities.

You have sacrificed nothing and no one.”

When confronted with those comments in an interview with ABC, Trump predictably went on the attack. He speculated that the Clinton campaign wrote those lines for him (in fact, he wrote the speech himself, and delivered it without notes—it was not loaded into the teleprompter). He called Khan “emotional” (though he added that he looked like a “nice guy”).

He implied that his wife Ghazala Khan was forbidden to speak: "She had nothing to say. Maybe she wasn't allowed to have anything to say. You tell me.”

She did speak. Ghazala Khan told Lawrence O'Donnell the night before Trump’s comments that she didn't want to speak at the convention because she still cries every time she sees a photo of her son. She also said this was the last thing she said to her son: "Don't become [a] hero for me. Just be my son. Come back as a son. He came back as a hero."

She spoke. Trump does not listen.

Trump did not express sympathy for their loss, he did not thank them for their son’s service. He attacked. Like McCarthy, it is the only way he knows to act. Every critic is an enemy who must be destroyed, not a human being to be engaged in dialogue. Such a person is utterly unfit to be president.

Trump’s willingness to snidely smear a Gold Star mother is perfectly in character for him. It puts on full display his utter lack of decency as a human being.

Joseph Welch asked the question that woke up the American people to Joe McCarthy’s lack of decency. Khizr and Ghazala Khan have done the same service for the American people today—if we listen.

______________________________________________

*President Eisenhower, who was appalled at McCarthy's attack on the Army, secretly provided the committee investigating McCarthy with a chronology undermining his attack on the Army.