Zachary Karabell is author of The Leading Indicators: A Short History of the Numbers That Rule Our World. He is a contributing editor at Politico Magazine.

“Have you no sense of decency, sir, at long last? Have you left no sense of decency?” Those cutting words, delivered on national television, effectively ended the career of Senator Joe McCarthy. For four years, McCarthy had enjoyed a kind of immunity as he smeared anyone he pleased while on a national witch hunt for Communist sympathizers. But in the spring of 1954, during hearings on supposed infiltrators in the U.S. Army that were broadcast on the new medium of television, McCarthy casually sought to destroy a young lawyer at the firm of Joseph Welch, counsel to the Army, an esteemed Harvard-trained lawyer and fellow Republican. When McCarthy suggested the junior attorney had Communist sympathies, the courtly Welch sank his head in despair, then looked McCarthy in the eye and excoriated him with those immortal words. Tens of millions of new American TV viewers watched in fascination and horror. The senator from Wisconsin never recovered.

Such turning points are not always evident when they happen: When does a nation reach a moment in which even a popular demagogue who has enjoyed a seeming immunity from public condemnation—no matter what he says—goes too far? History doesn’t repeat itself, and Donald Trump has defied many predictions of his downfall in the past. But it’s possible we may just have witnessed his McCarthy moment, considering the criticism that has been heaped on the GOP candidate from all sides in the past few days since Khizr and Ghazala Khan, the Pakistani-born American parents of an Army captain killed in the line of duty in Iraq in 2004, appeared at the podium of the Democratic National Convention to honor their son and make the case against Trump for president.


Khizr Khan’s short speech electrified the convention. “If it was up to Donald Trump,” Khan said, “[our son] never would have been in America ... Donald Trump, you're asking Americans to trust you with their future. Let me ask you: 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.”

As moving as Khan’s speech was, it’s what happened afterward that made the story explode. Trump, as is his wont whenever he is criticized, fired back at the Khans. In an interview, he oddly questioned why Ghazala Khan said nothing during the speech and implied that she may have not have been allowed to speak by her husband—a double hit on Muslims and women that only made Trump look worse when the mother later explained she simply couldn’t speak of her son Humayun without breaking down. Then Trump dug his own hole deeper. Asked by ABC’s George Stephanopoulos what sacrifices he, Trump, has made for his country, the GOP candidate appeared to compare Humayun Khan’s supreme sacrifice to … job creation. “I think I’ve made a lot of sacrifices. I’ve created thousands and thousands of jobs, tens of thousands of jobs,” Trump said. With some incredulity, Stephanopoulos responded: “Those are sacrifices?” Trump casually answered: “Oh sure, I think they’re sacrifices. I think when I can employ thousands and thousands of people, take care of their education, take care of so many things. Even in military, I mean I was very responsible, along with a group of people, for getting the Vietnam memorial in downtown Manhattan, which to this day people thank me for.”

Father of fallen Muslim-American war hero to Trump: “You have sacrificed nothing”

Khizr Khan’s response was full of raw fury. Sounding very much like a latter-day Joseph Welch, he declared of Trump: "He has no decency. He has a dark heart." Like his speech at the convention, those comments went viral too.

Are these two moments in history comparable? The nature of public shaming has changed dramatically in the past 60-odd years. In June 1954, the term “viral” had a very different meaning. And the nation appears to have become much more tolerant of outrageous speech. How much more tolerant is another question.

***

In that spring of 62 years ago, Senator Joe McCarthy, serving his second term as a Republican from Wisconsin, was arguably the most powerful political force in the United States. McCarthy had come to national prominence in 1950 when he charged that there were 200 known Communists who had infiltrated President Harry S. Truman’s State Department, and his subsequent investigations had morphed into a national hunt for Communist sympathizers. McCarthy and his committee were the leading edge of a “Red Scare” that cast a national pall over free speech, led companies large and small to dismiss employees on even a whiff of former flirtation with left-wing politics, and fueled widespread fear that in turn deepened the Cold War. There were, of course, some genuine spies and sympathizers, but the thousands unfairly implicated far dwarfed those numbers.

In 1954, McCarthy raised the stakes dramatically, raising suspicions about the loyalties of senior officials in the U.S. Army. The Army’s chief counsel, Joseph Welch, was a deeply respected 63-year old lawyer from Boston and a partner at the most white-shoe of white-shoe firms, Hale and Dorr. The Army had hired Welch, a registered Republican, to represent the service against accusations leveled by McCarthy that the Army was soft on Communism.

What made the Army-McCarthy hearings that began in April 1954 different was television. They were the first prominent congressional hearings televised, and at a time when there were a few channels, people watched what was on. That meant that 20 million people tuned in, and by some estimates tens of millions more, which was a significant portion of the U.S. population at the time. And on June 9, they witnessed the studious Welch turn the hearings on their head.

Simply being mentioned during these hearings was enough in those years to ruin someone’s career and potentially expose them to legal action and ostracism. Welch, who had been sparring with McCarthy and his chief counsel Roy Cohn for weeks, was visibly appalled when McCarthy sought to sully the young lawyer at his firm. “Until this moment, senator, I think I never really gauged your cruelty, or your recklessness," Welch said. "Little did I dream you could be so reckless and so cruel as to do an injury to that lad. It is, I regret to say, equally true that I fear he shall always bear a scar needlessly inflicted by you. If it were in my power to forgive you for your reckless cruelty, I would do so. I like to think I'm a gentle man, but your forgiveness will have to come from someone other than me ... You've done enough. Have you no sense of decency, sir, at long last? Have you left no sense of decency?”

For the first time, the bully had been called out in public by someone with no skeletons in his proverbial closet, whose integrity was unquestionable, and whose motives were purely patriotic. The audience in the senate chamber burst into applause. Coverage of the event was wildly supportive of Welch, and sharply critical of McCarthy. Within weeks, he was forced to bring the hearings to a close. His speeches over the summer, once front page news, were delivered to an empty, pre-CSPAN, Senate chamber. McCarthy, who had enjoyed positive support of half the country in January 1954, saw that fall to the low 30s in subsequent polls. Within months, his one-time allies had deserted him, and in December he was overwhelming rebuked and censured by the Senate by a vote of 67-22.

McCarthy served two meaningless years more in the Senate before dying of alcohol poisoning at age 48.

***

The coming days will determine whether Donald Trump has, like Joe McCarthy, crossed over some invisible line of decency that even many voters who now support him can’t stomach. In many ways the controversy is similar to past moments when Trump has attacked innocent people—like the judge in his Trump University case, Gonzalo P. Curiel, whom Trump impugned for his “Mexican heritage”—and was condemned for it, but still managed to keep his standing in the polls. This time could be different—even from when Trump insulted Sen. John McCain's war service, declaring that McCain was no hero because he was only captured, although the Arizona senator withstood torture for four years. Many predicted Trump’s downfall then too, and it didn’t happen.

But now Trump has touched a kind of ethical third rail by attacking the unimpeachable, suffering parents of a dead hero—Capt. Khan was awarded the Bronze Star for his actions—and by cheapening the very idea of sacrifice for one’s country. And with just 98 days left until the election, the GOP candidate's campaign is consumed in another unnecessary controversy—perhaps the biggest one yet—and Trump is being condemned by leading figures in both parties. Many in the military, which has given Trump a lot of support, are also questioning whether Trump is fit to be president. “I loathe Donald Trump with every fiber of my being,” one retired Army officer wrote on Facebook as the controversy took off. A group of Gold Star families organized by VoteVets.org wrote in an open letter published Monday: "When you question a mother's pain, by implying that her religion, not her grief, kept her from addressing an arena of people, you are attacking us. When you say your job building buildings is akin to our sacrifice, you are attacking our sacrifice." Brian Duffy, head of the 1.7-million-member Veterans of Foreign Wars, joined in, saying it was unacceptable for Trump to question the right of a Gold Star family member to exercise free speech. “There are certain sacrosanct subjects that no amount of wordsmithing can repair once crossed,” Duffy said.

McCain himself on Monday issued his harshest rebuke of the GOP candidate yet. ”While our Party has bestowed upon him the nomination, it is not accompanied by unfettered license to defame those who are the best among us," McCain said. "I'd like to say to Mr. and Mrs. Khan: thank you for immigrating to America. We're a better country because of you. And you are certainly right; your son was the best of America, and the memory of his sacrifice will make us a better nation—and he will never be forgotten." Representative Mike Coffman of Colorado, a Republican who served in combat as a Marine and represents a swing district in the Denver suburbs, told The New York Times that Trump had disrespected American troops. ”Having served in Iraq, I’m deeply offended when Donald Trump fails to honor the sacrifices of all of our brave soldiers who were lost in that war,” Coffman said. Ohio Gov. John Kasich, who battled Trump in the primaries, also suggested the candidate had abused the Khan family: “There’s only one way to talk about Gold Star parents: with honor and respect.”

Khizr Khan, meanwhile, has not let up in his counterattack on Trump. After he raised the stakes by asking senior Republican leaders, including House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell, to condemn Trump, they remained silent for a day before McConnell delivered an indirect rebuke to Trump, saying in a statement Sunday: "Captain Khan was an American hero, and like all Americans, I’m grateful for the sacrifices that selfless young men like Capt. Khan and their families have made in the war on terror. All Americans should value the patriotic service of the patriots who volunteer to selflessly defend us in the armed services.”

Trump’s campaign has desperately tried to contain the damage, issuing a statement of its own describing Humayun Khan as a “hero.” But the candidate himself battled on unrepentantly, tweeting on Sunday: “I was viciously attacked by Mr. Khan at the Democratic Convention. Am I not allowed to respond? Hillary voted for the Iraq War, not me!”

Trump has brought to the forefront of our national debate a range of real issues that any president and any who are drawn to public service will need to grapple with: economic insecurity, the challenge of terrorism, the miasma of immigration law, the frayed state of race relations, and disgust with political and financial elites who have promised the moon and delivered most to themselves and little to the rest. Those issues demand attention. But Donald Trump has churned up a great deal of darkness, and his moment may just have passed. Or not.