Turner, who served on the Cleveland City Council and in the state Senate, was an early backer of Hillary Clinton who switched to support Sanders and campaigned for him aggressively. While Sanders struggled to crack Clinton's support with black voters, Turner served as a surrogate who could credibly criticize Clinton's record on criminal-justice reform.
"Nina's got political cachet," said RoseAnn DeMoro, executive director of National Nurses United, a Sanders-supporting union that has not endorsed Clinton and that organized a small rally in support of Turner after she lost a speaking slot during the Democratic National Convention last week. "She killed herself for the last year in the Sanders campaign. She was the second to Bernie, I would imagine, in terms of speaking for the campaign on national television. She's African American, she's smart, she's a draw."
As most of Sanders's operation got behind Clinton, Turner was a prominent holdout. In an interview last month at the People's Summit, a post-Sanders campaign conference, Turner would not say whether progressives should support Clinton or a third-party candidate.
"A third party might not be bad for this country," she said. "Let's shake it up. We've had more than two parties over the history of our country. I know right now we have two, but maybe a third party might shake up both major parties. I'm a lifelong Democrat, but I want to see the Democratic Party live up to its principles. If we refuse to, if we are not able, then we do need to shake things up."
A month and a half later, Turner attended the Democratic National Convention as a Sanders surrogate, expecting to second his nomination for president. She was blocked by Clinton's campaign. That, and the roiling controversy over the Democratic National Committee's hacked emails, may have made Turner more receptive to the Green Party pitch.
"I don't know if Nina could have considered this a week ago," DeMoro said. "She felt shunned. She was shocked."
Stein, who only has held minor elected office in Massachusetts, has repeatedly tried to entice Sanders and his supporters into the Green Party. Since the New York primary, which Sanders lost in part because of onerous voter-registration requirements for Democrats, Stein has asked Sanders to have a conversation about the future of left-wing politics; since June, she has offered to give him a place on the Green Party ticket.
Sanders has rebuffed those calls, telling reporters that "either Hillary Clinton is going to become president or Donald Trump." Turner, who left her Senate seat for an unsuccessful bid for Ohio secretary of state, would be the second-highest-ranking politician ever to appear on a Green Party ticket. But the recent history of that move is not promising. In 2008, former congresswoman Cynthia McKinney (Ga.) bolted the Democratic Party and won the Greens' nomination for president. The result was the second-worst performance in party history, as the fourth presidential bid of Ralph Nader split the hard-left vote.
Nader did not run in 2012, and Stein, the party's presidential nominee that year, became its biggest vote-getter since the consumer advocate's 2000 Green bid. That still put the party in fourth place, behind the Libertarian ticket led by Gary Johnson; Stein's 2012 running mate, Cheri Honkala, resurfaced during the Democratic convention when she promoted an apparently failed "fart-in" of the convention hall.