Stephen K. Bannon, Donald Trump’s campaign chairman, at Trump Tower in New York on Aug. 20. (Carlo Allegri/Reuters)

ONE OF the most disturbing aspects of the presidential candidacy of Donald Trump is the legitimization it has provided for extremist discourse. Rhetoric that properly has been taboo in this country for a generation — overt racism, sexism, anti-Semitism — has begun to seep back into politics, with Mr. Trump and his closest associates providing cover. A telling example appeared this week in the form of a personal attack on the website Breitbart, whose executive chairman is Stephen K. Bannon, Mr. Trump’s campaign chairman. Its subject was Anne Applebaum, who is one of The Post’s most distinguished opinion columnists, a Pulitzer Prize-winning historian and — as the item repeatedly and gratuitously pointed out — a woman of Jewish origin.

Nominally a response to Ms. Applebaum’s writings about populist movements in Europe and their resemblances to the Trump campaign, the piece was written by an obscure Polish American writer who has an agreement with the foreign ministry of Poland’s right-wing nationalist government to assist with communications. He described Ms. Applebaum as manipulating a shadowy global network of journalists and commentators (including this editorial page) in order to slander the current regime in Warsaw, which has been accused by the European Commission, the Council of Europe and the Obama administration of endangering democratic checks and balances.

“Hell hath no fury like a Polish, Jewish, American elitist scorned,” proclaimed the Breitbart article. Anyone who doubts the intention of the Polish foreign ministry’s chosen propagandist in using those terms need only read the comments beneath the article, which — uncensored by Breitbart staff — reek with anti-Semitic slurs.

We sought Mr. Bannon’s reaction to his website’s publication of the article, and in particular to its identification of Ms. Applebaum as Jewish. The only response from an aide was that the Trump campaign chairman was on leave from the website. In other words, Mr. Bannon has no objection. Expect more openly anti-Semitic rants at his website — and, if Mr. Trump is elected, in the United States at large.