Seems like the Women’s Convention had trouble finding, uh, women.

Sen. Bernie Sanders, Independent of Vermont, will deliver the opening night address at the Women’s Convention, an event organized by the people behind the Women’s March rally earlier this year. The conference, which runs from October 27 to 29 in Detroit, is billed as a convention to show that “the rise of the woman IS the rise of the nation.” In practical terms, that means bringing together progressive grassroots organizations working on causes like economic and immigration reform for workshops and forums just before the 2018 midterm elections campaign heats up up.

“I think that right now, no one can deny that Bernie Sanders is probably one of the most powerful U.S. senators … on progressive issues, women’s issues, mobilizing millennials,” Tamika Mallory, a member of the Women’s March leadership, told USA Today. “He is really in line with the principles of the Women’s March.” She added that this was the first such event for women in four decades.

While the self-proclaimed “democratic socialist” is a favorite among leftwing millennials and activists—one poll even pegs him as the most popular politician in America—many liberal women have a complicated relationship with Sanders. That’s especially the case for females above 30, who overwhelmingly supported Hillary Clinton in last year’s Democratic presidential primary. Although he eventually endorsed and vigorously campaigned for Clinton in her match-up against Donald Trump, some—including the former Secretary of State— believe that the Senator dragged out his primary campaign and did unnecessary damage to the first woman to win a major party’s presidential nomination.

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Sanders’ “Bernie Bro” supporters, many of whom were white men, developed a reputation for trolling Clinton online. He also didn’t win fans by campaigning with a Democratic mayoral candidate in Nebraska who opposed reproductive rights. And then, there’s the fact that many think that the Women’s Convention should be headlined by a woman.

“I’m honored to join the women at the front lines of our struggle for economic, social, racial and environmental justice. In January, millions of women came out in an extraordinary and unprecedented display of power and resistance,” said Sanders in a statement. “Now more than ever, we must support the leadership of women across the country and fight together to advance our progressive agenda.” His office referred further questions to the organizers of the Convention.

The social media reaction was intense, with some blasting the convention’s organizers as sexist. MSNBC correspondent Joy-Ann Reid pondered if no woman was available, adding that “even the womens [sic] march movement is centering a man who dismisses women’s control of our own bodies as secondary.” One wag half-joked that Sanders was selected because Republican President Donald Trump and Senate majority leader Mitch McConnell, Republican of Kentucky, weren’t available. (Both men are viewed with hostility on the left.) Comments along the line of “a slap in the face for women” were also commonplace.

This story was updated with comment from Sen. Sanders.