“The Israeli people have the right to live in peace and security. So do the Palestinian people,” Sanders tweeted. “I remain concerned about the platform AIPAC provides for leaders who express bigotry and oppose basic Palestinian rights. For that reason I will not attend their conference.”

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His announcement cranked up to a boil a simmering left-right divide among American Jews over his candidacy.

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The split spans questions of whether and how to support Israel and what qualifies as anti-Semitism, those who study the community say. It includes a debate over whether Jewish ideals of justice are most urgently expressed through issues like universal health care, wage gaps and the environment, or by supporting and defending the Jewish state.

“Sanders is, for some Jews, the encapsulation of what they see as Jewishness. And to some he’s the antithesis,” said Yehuda Kurtzer, who studies Jewish identity as president of the Shalom Hartman Institute of North America.

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“Among involved Jews, I think he created a bigger problem for himself than he needed to,” Kurtzer said of Sanders’s decision to skip the annual Washington gathering of nearly 20,000 people. “He’s catering to a small percentage of his Jewish base that wants him to declare war on AIPAC.”

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AIPAC called Sanders’s tweet “truly shameful” and said its conference — which focuses on preserving U.S. support for Israel’s security — is “mainstream, bipartisan.”

Such debates are most important to affiliated Jews — the community center directors, synagogue presidents and rabbis from across the country who regularly attend the conference.

But American Jews are changing. And AIPAC’s bipartisan status is as well, with the lobbying group’s strong defense of Israeli security policies and embrace of Prime Minister Benjamin Netanyahu increasingly drawing criticism from Palestinian advocates and liberal Democrats.

A May Pew Research poll showed 42 percent of Jews believed the Trump administration favors Israel “too much” compared with the Palestinians. Forty-seven percent said the balance was about right. In 2013, a major Pew poll of U.S. Jews found 43 percent said caring about Israel is an essential part of being Jewish. But 38 percent of Jews under 30 said they were not very or not at all attached to Israel, compared with 23 percent of Jews over 50.

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Jews who do focus on Israel had strong reactions to Sanders’s move on AIPAC.

Mairav Zonszein, a writer who splits her time between Israel and the United States, tweeted that “Sanders is literally a hero for saying f--- you to AIPAC.” The post was liked 8,100 times as of Tuesday night.

“When he first started to rise in the polls, I thought — he should be the Jewish community’s favorite. You’d think: Finally someone who has all these social justice values,” Zonszein said. “But he represents the battle over what Jewish American values are on Israel. He represents this civil war.”

Jonathan Greenblatt of the Anti-Defamation League tweeted that Sanders’s announcement was “offensive,” especially given a national spike in anti-Semitism.

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“At a time when we see a surge of real hate across the US, it’s irresponsible to describe AIPAC like this. @ADL proudly will be there,” his tweet said.

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Sanders was asked in Tuesday night’s debate what he would say to Jews concerned by his choice. “I am very proud of being Jewish,” he answered, before calling Netanyahu “a reactionary racist.”

“I happen to believe that what our foreign policy in the Mideast should be about is absolutely protecting the independence and security of Israel. But you cannot ignore the suffering of the Palestinian people.”

Sanders has also taken heat from some Jewish leaders for his welcoming of support from freshman Reps. Ilhan Omar (D-Minn.) and Rashida Tlaib (D-Mich.), strong critics of Israel who support a controversial boycott movement. Sanders does not support the boycott effort.

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Multiple Jewish groups reacted to Sanders’s AIPAC decision by emphasizing unity and dialogue.

“If Sen. Bernie Sanders wants to lead the Democratic Party and the nation, I hope he can speak to, engage with, and even debate everyone,” tweeted Rabbi Rick Jacobs, head of the Reform Movement, the largest denomination of Judaism in the United States.

But U.S. Jews are less affiliated with denominations and institutions than other faith groups. One third say they are not part of any Jewish denomination, Pew found in 2013. They may not particularly care whether Sanders, a frequent critic of Israel’s treatment of Palestinians, speaks at AIPAC.

The organization in previous decades was seen as less partisan. But its strong support for Netanyahu during the Obama administration, even as the two leaders clashed over settlements and the Iran nuclear deal, thrilled Republicans and offended many Democrats.

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In 2016, some conference attendees gave a raucous welcome to then-candidate Donald Trump, who slammed both President Barack Obama and Hillary Clinton in his remarks. Hundreds had walked out in protest when Trump took the podium.

Sanders, who was also a candidate that year, declined to attend the conference but sent a video. AIPAC had allowed candidates in the past to address the conference that way. But the group said it had changed its policy and declined to play Sanders’s message.

Liberal groups critical of Israel have pressured Democratic candidates to skip this year’s conference. Sen. Elizabeth Warren (Mass.) told a questioner before the New Hampshire primary that she is not going; Sen. Amy Klobuchar (Minn.) and former South Bend, Ind., mayor Pete Buttigieg say they have scheduling conflicts. Former New York mayor Mike Bloomberg, who also is Jewish, will speak at the conference. It was not clear Wednesday whether former vice president Joe Biden will attend.

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Sanders has been reluctant to discuss his personal life on the campaign trail, though he has opened up recently about his Jewish heritage. He ties the deaths of relatives in Nazi Europe to his fight for immigrants and his stance against white nationalism since President Trump took office.

His campaign did not return an email request to discuss the AIPAC decision. But he has styled himself as an insurgent, calling for radical change. So upsetting some Jewish leaders and institutions may not be a major concern to him.

Nor do Jews appear to be a key part of Sanders’s base. The most recent data, from Pew in January, had just 11 percent of U.S. Jews picking Sanders as their top choice.

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Jeremy Burton, head of the Jewish Community Relations Council of Greater Boston, said he’s heard responses to Sanders’s decision that are all over the map.

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The one common theme, he said, is anxiety among Jews about having a Jewish nominee or president. That’s true whether the person is Sanders or Bloomberg.

“At the end of the day, Jews know anti-Semitism is part of the DNA of Western civilization,” Burton said. “And when people are despairing or feeling at a loss, somehow Jews will get blamed.”

Correction: An earlier version of this story misstated the findings of a May Pew Research poll on the percentage of Jews under 30 who said they were not very or not at all attached to Israel. The story has been corrected.