Mayor Bloomberg delivered his first big scoop of the election — emerging as the first and only Democratic candidate to go personally before the annual conference of the American Israel Public Affairs Committee. He delivered a speech brimming with standard pro-Israel promises. In the context of his party’s primary, though, it was a blunt riposte to, in Senator Sanders, a front-runner who is hostile to the Jewish state. We don’t mind saying that it was a terrific thing for Hizzoner to do.

Mr. Bloomberg opened at Aipac by commenting on how wonderful it was to be with the leading pro-Israel group. He noted its diverse bipartisan membership, including Christians as well as Jews. “At a time when some try to make strong supporters of Israel feel unwelcome in social justice conversations, your refusal to be intimidated reminds us of the courage and integrity that we need in our political discourse,” Mr. Bloomberg said.

It couldn’t have been a more pointed dig at Mr. Sanders, who, as a young man, briefly lived on an ultra-left-wing kibbutz that celebrated Stalin. Just to mark the moment, though, Mr. Bloomberg made a point of reiterating his opposition to the boycott, divestment, and sanctions movement that is one of the main wedges being used against Israel by today’s left, including some rising Democrats in Congress, such as Alexandria Ocasio-Cortez and Ilhan Omar.

Nor did Mr. Bloomberg stop there. The ex-mayor of New York referred to Jerusalem as the “eternal capital of the Jewish state.” He also backed President Trump’s decision to enforce the law passed by Congress to move the American embassy in Israel to Jerusalem from Tel Aviv. He would leave the embassy in Jerusalem, he said, because “that’s where it belongs.” The vow evoked what Newsweek called loud applause. Mr. Sanders said in Charleston that he would take moving the embassy out of Jerusalem under consideration.

What strikes us about Mr. Bloomberg’s speech at Aipac is that it’s what he should have done on all the other issues on which he’s been retreating in the campaign. Rather than apologize for stop, question, and frisk, he should have marked its original intent — to protect minority communities being ravaged by crime. Instead of lifting the confidentiality of the settlements his company may have struck on sexual harassment, he should have stood by them.

The betting is that it is too late for him to save his campaign, no matter how much he has to spend. Even if he finds it within himself to stand up to the Democratic pack, can he find it within himself to confront the President during the general election? We don’t know the answers to those questions. We did, though, find his appearance at Aipac to be, in the circumstances, a newsworthy move. That kind of gumption is why there was a constituency for him to get into the race.