Sen. Bernie Sanders (I-Vt.) is declining to join a progressive group he co-founded in encouraging Michigan voters to spurn President Joe Biden over his support for Israel’s assault on Gaza.

Our Revolution, a nonprofit that grew out of the progressive icon’s 2016 presidential campaign, backed the effort to get voters in Michigan to vote “uncommitted” in the state’s Feb. 27 presidential primary as a way to protest Biden’s support for the war, which was launched in response to the Oct. 7 attack by the militant group Hamas in which about 1,200 Israelis were killed and about 250 people were taken hostage. Israel’s assault on Gaza has so far led to the deaths of more than 28,000 Palestinians, according to local health officials.

In a statement to HuffPost, Sanders’ office said he was supporting Biden even though he continues to break with the administration over Gaza, including voting against a Biden-backed bill to toughen border security and send aid to Ukraine because the package also included military aid for Israel.

“Our Revolution is a completely independent organization and the Senator had no part in their decision,” Sanders spokeswoman Anna Bahr said in a statement. “Bernie is supporting the President’s re-election and wants him to do well in the Michigan primary and elsewhere.

“It is no secret, however, that Bernie disagrees with the Administration’s position on the war in Gaza. He strongly opposes providing the right-wing Netanyahu government with the $10 billion in the foreign aid supplemental to continue its horrific war against the Palestinian people.”

The decision by Sanders, who is Jewish, shows how the war in Gaza, and Biden’s handling of it, has split both the progressive movement and the Democratic Party more broadly. Polling has shown Democrats are increasingly skeptical of the right-wing Israeli government’s brutal bombing campaigns, and many Muslim Democrats and progressives have said they would struggle to support Biden if he continues to back the military campaign.

The split between Sanders and Our Revolution in part shows a divide over how best to win those voters back.

Former Rep. Andy Levin (D-Mich.), a Jewish Democrat who lost his seat after super PACs backed by the American-Israel Public Affairs Committee targeted him over his opposition to expanded Jewish settlements in the West Bank, told The New York Times he was backing the “uncommitted” campaign to help Biden.

“I am working with some people who feel like they will never vote for Joe Biden, but there are many, many, many I feel will vote for Joe Biden on Nov. 5 if he changes course,” Levin told the paper. “This is the best way I can help Joe Biden.”

Levin was the signatory on an email Our Revolution sent out to its members on Wednesday morning. The group also plans to reach out to its 87,000 members in Michigan with phone banks and events on the state’s college campuses. An official of the group told the Times that they hope 10% of the state’s voters back “uncommitted.”

Michigan is being targeted because of the state’s comparatively large Muslim and Arab American populations, where Biden’s support for Israel has been deeply unpopular. Local elected officials in the state have organized a separate effort to encourage an “uncommitted” vote.

Among the leaders of the campaign, called “Listen to Michigan,” is Layla Elabed, the younger sister of Rep. Rashida Tlaib (D-Mich.). Tlaib, the only Palestinian American in Congress, has yet to endorse Biden’s campaign.

“Michigan voters are sending Biden a clear message in the February 27 Democratic primary that he can count us out. We are filling out the UNCOMMITTED bubble because we strongly reject Biden’s funding war and genocide in Gaza,” the group’s website says. “Biden must earn our vote through a dramatic change in policy.”

Sanders, however, isn’t the only progressive sticking with Biden. Rep. Alexandria Ocasio-Cortez, like Tlaib a member of the progressive “Squad” in the House of Representatives, stood by her endorsement in a Tuesday CNN interview.

“I know who I’m going to choose,” she said, citing Biden’s work to pass climate change and economic recovery legislation. “It’s going to be one of the most successful presidents in modern American history.”