BY LAURA KELLY – 03/01/20 12:03 PM EST

The leader of one of the largest pro-Israel lobbying groups in the U.S. promised Sunday to “defeat” political movements seen as threatening the relationship between the U.S. and Israel, a veiled attack against Democratic presidential candidate Sen. Bernie Sanders (I-Vt.).

Howard Kohr, CEO of the American Israel Public Affairs Committee (AIPAC), opened the organization’s annual conference in Washington D.C. by issuing a stark warning to push back against “political leaders and their supporters” who call for conditions on U.S. support for Israel.

Sanders is the only candidate in the Democratic presidential race to raise the issue of conditioning military aid to Israel. 

“We face a collection of political leaders and their supporters who want to turn our political system away from Israel,” Kohr said to the 18,000 attendees at the start of the three-day conference.

“The pro-Israel community will work to defeat those who try to harm our friends, and those who try to harm the U.S.-Israel relationship.”

The shot at Sanders speaks to the lead the self-described democratic socialist has over the other Democratic presidential candidates. Despite coming in second to former Vice President Joe Biden in the South Carolina primaries, Sanders has proven a formidable competitor with primary wins in Nevada, New Hampshire and a tight second place in Iowa.

Sanders describes his political movement as aligning with progressive values. In foreign policy, he advocates against military intervention and in support of global diplomatic engagement.

Progressive groups critical of the U.S.-Israel relationship have pushed Democrats and Democratic presidential candidates to leverage U.S. assistance to Israel to push back on policies they view as impediments to resolving the Israeli and Palestinian conflict.

Sanders has separated himself from other Democratic presidential candidates by raising the possibility of conditioning military aid to Israel over its policies towards the Palestinians and moving the U.S. embassy back to Tel Aviv from Jerusalem as something he would “take into consideration.”

“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,” he said last month during the Democratic presidential debate in South Carolina.

Kohr on Sunday attacked those views as misleading.  

“The leaders of this movement occasionally seek to mollify us with empty reassurances and hallow affirmations of Israel’s right to live in peace. But far too often they reveal their true beliefs,” he said.

“The leaders of these movements say they support Israel’s right to exist, but that’s not up for debate. Israel exists.”

AIPAC, which stresses its mission as ensuring bipartisan support for a strong U.S. and Israel relationship, advocates that Congress maintain $3.3 billion in foreign military financing to the Jewish State without conditions.

“America’s security support for Israel should never, never be used as a bargaining chip in the US, Israel relationship,” Kohr said.  

“And we are grateful that overwhelming majorities of Democrats and Republicans in Congress have consistently supported Israel security, without conditions, and without hesitation.”

Sanders has clashed with the organization in recent days, slamming AIPAC as providing a platform to speakers who “express bigotry and oppose basic Palestinian rights.” He rejected attending the conference where nearly all other Democratic candidates have offered to provide remarks.

AIPAC responded by calling Sanders’s remarks “outrageous” and “truly shameful.”

Democratic presidential candidate Senator Elizabeth Warren (D-Mass.), who also aligns herself with progressive the progressive wing of the party, was the only other candidate to publicly commit to skipping the AIPAC conference.

Only one Democratic presidential candidate will address the conference in person, former New York City Mayor Mike Bloomberg, as it coincides with primary races across the U.S.

Nearly all other candidates offered pre-recorded video messages to address the conference.

Sen. Amy Klobuchar (D-Minn.) said in her video message on Sunday that she is committed to a two-state solution to the Israeli and Palestinian conflict, security assistance to Israel and opposes efforts to delegitimize and boycott the Jewish State.

“I will never stop fighting for a strong US-Israel relationship. Period,” she said. “I am also committed to a peace process that can lead to a two state solution that allows Israelis and Palestinians to live side by side in peace and security.”

Video messages from former Vice President Joseph Biden and former mayor of South Bend, Ind., Pete Buttigieg, will also air at the conference.

AIPAC has yet to announce if it has a video message from Rep. Tulsi Gabbard (D-Hawaii).