For the second time in barely a year, a contestant on Donald Trump’s TV show “The Apprentice” has made an anti-Semitic remark. And once again, the offender was not penalized for doing so.

On this week’s episode, Clay Lee, a 28-year-old Texas real estate agent, explains (in front of an audience) that his Jewish teammate, Adam Israelov, was cheap on a date because Adam is a “tight Jewish boy.” Clay’s later apology seems half-hearted, and with Adam out of the room, he blames Adam for being overly sensitive, asserting that Adam “needs to learn to relax.”

With tens of millions of Americans watching, this was an opportunity for Trump to send the obvious message that bigotry is unacceptable in American society and people who make bigoted remarks cannot work for him.

Sadly, Donald didn’t do it.

In the boardroom meeting (where Trump decides which contestants should be fired), Trump’s adviser George Ross agrees that Clay’s statement was “totally insensitive,” and recommends that he be fired since “the key to a good executive is sensitivity to people.”

Adam, for his part, reveals that Clay has made more than just one offensive comment about Jews. At the same time, Adam says he “does not believe [Clay] is anti-Semitic.”

Trump follows: “Clay, I really believe that you are not anti-Semitic. I felt very relieved when Adam said he believed you were not anti-Semitic. Because you’ve gone through a lot, being gay. And you’ve gone through your own form of discrimination.”

Whatever the depth of Clay’s sentiments about Jews — and who can measure that precisely? — a sophisticated business leader like Donald Trump should be able to recognize bigotry when he hears it, and bigotry should be grounds for dismissal. Instead, Trump fires a third contestant, Markus, whom he found annoyingly verbose. “You always use too many words, just too long, too long … Just too much talk.”

Talking too much gets Markus fired. Talking against Jews doesn’t get Clay fired.

It didn’t get Jennifer Crisafulli fired, either. On an episode of “The Apprentice” last October, Ms. Crisafulli blamed her team’s loss in a particular task — running a restaurant for one day — on the fact that “two old Jewish fat ladies” had given her team low ratings.

On that show, Trump did fire Crisafulli, but not because of her bigotry; in fact, he did not mention her anti-Jewish remark during their boardroom discussion. Trump’s perfect chance to discredit anti-Semitism was missed.

But Crisafulli’s real-life employer, the real estate agency Prudential Douglas Elliman, did not miss the opportunity. It immediately fired her for her bigoted statement. Too bad Trump did not learn a lesson from fellow real estate agents.

A few remarks about “tight Jews” or “old Jewish fat ladies” do not a Holocaust make. But when they are so pointedly excused on national television, they become part of the process by which American society sets its cultural standards and determines the threshold for tolerating bigotry.

Zero tolerance is the morally right stand to take. And in a world where serious anti-Semitism — sometimes violent anti-Semitism — is growing, it becomes all the more important that a powerful figure like Donald Trump does the right thing.

One of New York City’s greatest mayors, Fiorello LaGuardia, understood this as well as anyone, and better than most. In March 1944, with anti-Semitism rising in the city (not to mention around the country), LaGuardia ordered his city commissioners to forbid municipal employees from “associating or fraternizing” with known anti-Semites. However many employees were directly affected by the new regulation, its real power lay in the principle that LaGuardia was articulating. Anti-Semites were pariahs.

Donald Trump’s words carry considerable weight, in business and more lately in the world of reality TV. He should have said to Clay — just as he should have said to Jennifer Crisafulli last year:

“There is no room in my company for someone who makes anti-Semitic statements.

“You’re fired!”

Rafael Medoff and Benyamin Korn are director and associate director, respectively, of the David S. Wyman Institute for Holocaust Studies, which focuses on issues related to America’s response to the Holocaust.