The attempt by students at New York University to blame Chelsea Clinton for the massacre of Muslims in New Zealand is a shocking marker of the temper of our times. At a vigil for the 49 persons killed by a self-described “racist” and “ethno-nationalist eco-fascist,” students accused Ms. Clinton of having stoked the killer’s hatred because — wait for it — she recently criticized anti-Semitism.

If that sounds crazy, feature the video that has gone viral on Youtube. It shows Ms. Clinton, visibly pregnant and backed against a wall, being told — by a woman jabbing a finger at her — “Forty-nine people died because of the rhetoric you put out there.” It was apparently a reference to Ms. Clinton’s condemnation of the anti-Jewish remarks of, among others, Congresswoman Ilhan Omar.

To defend Jews, it seems, is itself deemed a hostile act. Ms. Clinton, taken aback by the accusation against her and the hostile tone of her accuser, reacted with more grace and politeness than the woman attacking her deserved. She put her hands to her heart and said, “I’m so sorry you feel that way.” Her accuser then gestured to what appears to be the vigil itself.

“This right here,” Ms. Clinton’s accuser shouted, “is the result of a massacre stoked by people like you and the words that you have put out. And I want you to know that and I want you to feel that deep inside. Forty-nine people died because of the rhetoric you put out there.” When Ms. Clinton apologized, a male, from off camera, shouted, “What does ‘I’m sorry you feel that way’ mean?”

One of the highest profile figures to spring to Ms. Clinton’s defense was Donald Trump Jr. “It’s sickening to see people blame @ChelseaClinton for the NZ attacks because she spoke out against anti-Semitism,” he tweeted. “We should all be condemning anti-Semitism & all forms of hate. Chelsea should be praised for speaking up.” Good for him.

How, though, did that go down? According to the Washington Post, the president of the Center for American Progress, Neera Tanden, a longtime Clinton ally, accused the junior Mr. Trump of trying to sow discord among Democrats, tweeting: “The right wants to exploit disputes in the Center-Left.” It’s gotten to the point where a leader of the center-left intelligentsia can’t even find it within herself to accept a message defending Ms. Clinton — if it’s from a Trump.

We’re tempted to call all this Ms. Clinton’s own Sister Souljah Moment. That’s a reference to the famous incident in 1992, when presidential candidate Bill Clinton rebuked the political activist Sister Souljah for asking, after the Los Angeles riots that year, “why not have a week and kill white people?” Mr. Clinton had suggested her words were analogous to the language of the Ku Klux Klan leader David Duke.

Saying that helped Mr. Clinton win the presidency in 1992. His daughter was as right as rain to call out anti-Semitism. Her doing so played no role whatsoever in inspiriting the white racist who murdered 49 innocent Muslims at Christchurch, New Zealand. Neither, contra-Senator Richard Blumenthal and others, did President Trump. It would be a tragic thing if our divided leaders can’t come together to denounce the actual perpetrator of that ghastly crime.