Daniel Biss, an Illinois state senator seeking the Democratic gubernatorial nomination, dropped Chicago Alderman Carlos Ramirez-Rosa as his running mate on Wednesday over Ramirez-Rosas criticism of Israel and affiliation with a group that supports the Boycott, Divestment and Sanctions movement.

The incident served as a reminder that, while the surge in progressive activism ushered in by the presidential campaign of Sen. Bernie Sanders (I-Vt.) has moved Democrats to the left on many economic issues, the spectrum of acceptable debate about the Israeli-Palestinian conflict remains relatively narrow.

I was hopeful that this campaign could have recognized our differences and come together to focus on those key progressive issues that are important to Illinoiss working families. And unfortunately, that did not occur, Ramirez-Rosa told HuffPost. My hope is that five years from now, as a Democratic Party , we are more committed to having these constructive dialogues and allowing for these differences to exist.

Bisss selection of Ramirez-Rosa as his candidate for lieutenant governor last Thursday sparked an outpouring of excitement from progressive activists and organizations. At 28, Ramirez-Rosa is Chicagos first openly gay Latino alderman and one of the countrys most prominent members of the Democratic Socialists of America. Thanks in no small part to Sanders, who calls himself a democratic socialist, DSA has seen its dues-paying membership nearly quadruple, to more than 28,000, since the November election. Ramirez-Rosa, who joined in February, has become the organizations closest thing to a political celebrity.

But Ramirez-Rosas affiliation with DSA, which has endorsed the Boycott, Divestment and Sanctions (BDS) movement against Israel, immediately created a political headache for Biss.

Ramirez-Rosa, who served as a Democratic National Convention delegate for Sanders in July 2016, has also spoken out against what he considers the United States sponsorship of the Israeli occupation of the Palestinian territories Israel conquered in 1967.

You know, for too long the U.S. government has subsidized the oppression of the Palestinian people, and its time that thats stopped, Ramirez-Rosa told the left-wing Real News Network in June 2016 . And we have seen a shift internationally in favor of justice for the Palestinian people. You know, people stand with Israel, but they also want to make sure the Palestinian people have [justice].

Rep. Brad Schneider (D-Ill.), a moderate who represents affluent Chicago suburbs, withdrew his endorsement of Biss in a note on Facebook on Sunday, citing Ramirez-Rosas tough criticism of Israel and membership in DSA. Schneider is an active member of the American-Israel Public Affairs Committee, a hawkish and influential pro-Israel lobby, and pro-Israel groups were his third-largest category of donors in 2016.

Biss responded by demanding that Ramirez-Rosa unequivocally denounce BDS or leave the ticket, according to a source with knowledge of their conversations.

After several days of discussions, Ramirez-Rosa announced his departure from the ticket, claiming in a Facebook message that his difference of opinion with Biss on BDS at the federal rather than state level had proved insurmountable. (In an interview with HuffPost, Ramirez-Rosa would not confirm the details of their talks, citing his commitment to their shared privacy.)

Ramirez-Rosa said he refuses to condemn BDS in all its forms because he believes that it is part of a constructive dialogue about how the United States should leverage its power on the global stage to end the Israeli occupation of the West Bank, Gaza and East Jerusalem.

Im not going to throw a nonviolent movement under the bus or impugn their aims or impugn their tactics, he told HuffPost. Amongst the international community and within the United States, there is a broad agreement that we need to end the occupation of Palestine, that we need a solution that recognizes the humanity of both the Israeli and the Palestinian people.

Such a solution must also recognize 4,000 years of anti-Semitism, he added.

At the same time, Ramirez-Rosa does not support state governments boycotting Israel, since foreign policy is a federal matter.

When asked by HuffPost if, in his capacity as lieutenant governor, he would have visited Israel as part of a state government delegation, Ramirez-Rosa affirmed that he absolutely would have.

Ramirez-Rosa said he remained supportive of a two-state solution in which a Palestinian state would exist alongside Israel. He has not adopted the far lefts preference for the creation of one binational state between the Jordan River and the Mediterranean Sea.

Biss, who is Jewish and whose mother is Israeli, said in a statement about Ramirez-Rosas departure that he believes BDS moves us further away from a peaceful solution.

He also accused Ramirez-Rosa of failing to be upfront about his views on the matter.

When I asked him in the interview process prior to his selection, Carlos said he too supported a two-state solution and opposed BDS, Biss wrote. After much discussion, its become clear that Carlos position has changed. While I respect his right to come to his own conclusions on the issue, it simply wasnt the understanding we shared when I asked him to join the ticket.