Florida Rep. Lois Frankel, a Jewish Democrat, quit the party’s progressive caucus, one of the largest in  Congress, as the Israel-Hamas war has brought to the surface long simmering differences over Israel among progressives.

Frankel’s departure was first reported Monday by The Intercept, and later confirmed with her office by Axios. Both publications cited anonymous sources as saying that Frankel quit over how progressives were treating Israel since Hamas terrorists invaded the country on Oct. 7, launching a war.

The Congressional Progressive Caucus, which numbers 100 or so members out of the 212 Democrats in the U.S. House of Representatives, has long avoided Israel issues to keep the peace among members. Frankel, Axios reported, has a 96% rating of voting with the progressive agenda on issues not related to Israel.

In the weeks since the war, Frankel, along with other Jewish Democrats, has pushed back bids by other progressives to condemn Israel’s wartime conduct and to call for a ceasefire.

Earlier this month, she was one of six progressives among 22 Democrats who joined Republicans in censuring Palestinian American Michigan Rep. Rashida Tlaib for sing pro-Palestinian language that some Jewish groups say is antisemitic. Two other progressive caucus members voting to censure Tlaib are Jewish: Steve Cohen of Tennessee and Dan Goldman of New York.

Israel has long been a fault line among progressives, but it has not riven the caucus until now. Members of the caucus’s small left wing, the “Squad,” which includes Tlaib, have led calls to defund assistance to Israel and since the war to call for a ceasefire. Others, like Ritchie Torres of New York — who also voted to censure Tlaib — have vigorously defended Israel as a pluralistic democracy and have accepted the endorsement of the American Israel Public Affairs Committee, which Tlaib and others have made a bogeyman.

Tensions among progressives occasionally burst to the surface, for instance in July, when the caucus chairwoman, Rep. Pramila Jayapal of Washington, sought to calm a crowd at a Netroots Nation conference in Chicago that protested that members of the caucus were not outspoken enough in their criticism of Israel. The protests brought a panel to a standstill for more than 20 minutes.

A specific target of the protests at that conference was Illinois Rep. Jan Schakowsky, who is Jewish. “Maybe I should just walk off,” she said, until Jayapal urged her to stay.