Mainstream US Jewish groups reacted with outrage on Monday to what they saw as 2020 Democratic presidential candidate Bernie Sanders’ “offensive” attack on the American Israel Public Affairs Committee, as the hashtag #AIPACProud went viral on Twitter in protest.

Sanders — who has emerged the frontrunner in the ongoing contest for the Democratic nomination — tweeted on Sunday that he would not attend AIPAC’s upcoming annual conference in Washington, DC, because he was “concerned about the platform AIPAC provides for leaders who express bigotry and oppose basic Palestinian rights.”

The senator gave no indication as to who these leaders were or what they had, in fact, actually said.

As a barrage of criticism came down on Sanders under the hashtag #AIPACProud, major Jewish groups and their leaders expressed anger and pain at the longtime Vermont senator’s statement.

Related coverage Deputy PM Says Time Is Right for Spain to Become a Republic Spain's far-left deputy prime minister said on Saturday that a financial scandal which has rocked the royal family had presented...

The Conference of Presidents of Major American Jewish Organizations called Sanders’ words “irresponsible and counterproductive,” saying, “AIPAC brings together a bipartisan diversity of all sectors of society from across the political spectrum.”

@AIPAC brings together a bipartisan diversity of all sectors of society from across the political spectrum. Boycotting this important opportunity for dialogue is irresponsible and counterproductive. We advise our member organizations to join us in attending. #AIPACproud — Conf Of Presidents (@Conf_of_Pres) February 24, 2020

Jonathan Greenblatt, CEO of the Anti-Defamation League (ADL), characterized Sanders’ claim as “offensive” and accused him of encouraging antisemitism, saying, “At a time when we see a surge of real hate across the US, it’s irresponsible to describe AIPAC like this.”

It’s offensive that @BernieSanders denigrates the @AIPAC policy conference as a platform for bigotry. 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. https://t.co/MlK4SgYHfL — Jonathan Greenblatt (@JGreenblattADL) February 24, 2020

The American Jewish Committee (AJC) tweeted, “We flatly reject Senator Sanders’ smears of @AIPAC and will attend its Policy Conference in greater numbers than ever before. We are #AIPACProud.”

We flatly reject Senator Sanders’ smears of @AIPAC and will attend its Policy Conference in greater numbers than ever before, led by our CEO, @DavidHarrisAJC. We are #AIPACProud.https://t.co/PCi1PVBEWh — American Jewish Committee (@AJCGlobal) February 24, 2020

The AJC’s head, David Harris, addressed Sanders personally, saying, “You won’t address 18,000 Americans of all backgrounds celebrating US-Israel ties. Shame. You overlook core interests & values at heart of USIL link. Shame. You describe #AIPAC as a platform for bigotry. Shame. You ignore AIPAC’s support for 2-state deal. Shame.”

Sen. Sanders, You won’t address 18,000 Americans of all backgrounds celebrating US-Israel ties. Shame. You overlook core interests & values at heart of 🇺🇸🇮🇱 link. Shame. You describe #AIPAC as a platform for bigotry. Shame. You ignore AIPAC’s support for 2-state deal. Shame. https://t.co/zMSfUykj0c — David Harris (@DavidHarrisAJC) February 24, 2020

Rabbi Rick Jacobs — the president of the Union for Reform Judaism — accused Sanders of being unwilling to embrace diversity, stating, “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. Don’t skip AIPAC; speak to — and with — participants at AIPAC.”

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. Don’t skip AIPAC; speak to—and with—participants at AIPAC. https://t.co/VcGbIanpxQ — Rabbi Rick Jacobs (@URJPresident) February 24, 2020

The Jewish Democratic Council of America (JDCA) emphasized continuing support for Israel among Democrats, saying, “We are participating in AIPAC Policy conference, along with many other Democrats, including members of Congress.”

“We welcome the opportunity to come together with others with a wide range of views to express the importance of the US-Israel relationship, which has been and must remain a bipartisan issue,” it added.

AIPAC itself was uncharacteristically strident in its reaction to Sanders’ broadside, saying in a statement, “Senator Sanders has never attended our conference and that is evident from his outrageous comment.”

“In fact, many of his own Senate and House Democratic colleagues and leaders speak from our platform to the over 18,000 Americans from widely diverse backgrounds — Democrats, Republicans, Jews, Christians, African-Americans, Hispanic Americans, progressives, Veterans, students, members of the LGBTQ+ community — who participate in the conference to proclaim their support for the US-Israel relationship,” the group pointed out.

“By engaging in such an odious attack on this mainstream, bipartisan American political event, Senator Sanders is insulting his very own colleagues and the millions of Americans who stand with Israel,” it concluded. “Truly shameful.”