Green Party presidential candidate Jill Stein speaks to Bernie Sanders supporters outside City Hall in Philadelphia on July 2. (Michael Robinson Chavez/The Washington Post)

Over profanities about the Democratic Party on Tuesday, a chant rang out across a downtown plaza: “Jill, not Hill!”

And then, from behind a 30-foot bronze sculpture that goes by the title “Government of the People,” the woman herself emerged: Jill Stein, the presumptive presidential nominee of the Green Party and the final frontier for loyalists of Bernie Sanders who refuse to vote for Hillary Clinton.

Her index finger pressed to her thumb, Stein prosecuted the case against both major political parties, saying it was impossible to have a revolutionary movement within a “counterrevolutionary party.” She accused Clinton, who later in the day became the Democratic presidential nominee, of “backstabbing” Sanders — and she beckoned to his angry supporters with a promise of salvation: “My campaign is here.”

Stein, 66, a physician-turned-political activist, is trying to seize on Democratic divisions that flared as the convention began, to lure liberals who feel abandoned now that Sanders has officially lost, leaving them without a preferred candidate. On the streets of Philadelphia this week, Stein has been, in effect, shadowing the Sanders backers, creating a buzz among some here that she offers a credible alternative for those who want to vote but can’t stand the thought of siding with Clinton or Republican Donald Trump.

That’s exactly what worries many Democrats here. In Stein, they are starting to have flashbacks to 2000, when Ralph Nader ran an insurgency from the left that many still blame for costing Al Gore the election.

On the second night of the Democratic National Convention in Philadelphia, delegates supporting Sen. Bernie Sanders (D-Vt.) walked out in protest, despite Sanders's calls for unity within the party. (Peter Stevenson,Adriana Usero,Dalton Bennett,David Bruns,Jayne Orenstein,Alice Li/The Washington Post)

“I’m sure she’s a great person, but I can’t see how the effort can lead to anything but helping Trump,” said Rep. Keith Ellison (Minn.), who had been one of Sanders’s most high-profile supporters but is now urging the party to unify behind Clinton. “Trump is such a clear and present danger to the republic that we’ve got to get behind the candidate who gives us the best chance of defeating Trump.”

Stein said Tuesday that she’s not worried about shouldering the blame if Clinton loses in November.

“I am very worried about whether Donald Trump gets elected or whether Hillary Clinton gets elected,” she told reporters.

She said that she hasn’t spoken with Sanders, and that she continues to urge him to “get in touch,” adding that Clinton’s campaign probably is “not interested in talking to us.”

A two-time Harvard graduate from Lexington, Mass., Stein practiced internal medicine for 27 years before turning to political activism full time, focusing on environmental and health issues in particular. She entered numerous political races in Massachusetts, and was elected to a local town seat in Lexington in 2005. She made her first bid for the White House in 2012, as the Green Party’s candidate, and netted less than 1 percent of the vote.

Her running mate in that campaign, Cheri Honkala, said Stein saw herself as jump-starting a “movement for political independence,” and didn’t care about their impossible odds.

Stein is an evangelist of healthful eating, said Honkala, recalling that her clearest image of her former running mate is with blueberries stuck between her teeth.

Stein is expected to name a No. 2 as the Green Party convention approaches in August.

She may not do much better in 2016, political scientists predicted.

In addition to the structural obstacles faced by third parties, Clinton has moved decisively to the left, said Lawrence Jacobs, a political scientist at the University of Minnesota. Less concerned about losing centrist voters to Trump, Jacobs said, Clinton made concessions to fend off Sanders’s insurgent campaign and then, more recently, to ensure that he would endorse her. This blunts Stein’s appeal, he said.

“She’s trying to swim upstream even though there’s a Hoover Dam in front of her and it’s just been reinforced with a second Hoover Dam,” he said.

And yet Hans Noel, a political scientist at Georgetown University, warned that minor support nationwide may not prevent her from tipping the balance in a swing state, as Nader did in Florida in 2000.

A July Washington Post-ABC News poll found that 14 percent of registered voters said they would seriously consider a third-party candidate but that only 2 percent specifically named Stein. When voters in the same survey were presented with named options — Clinton, Trump, Stein, and libertarian Gary Johnson — Stein received 5 percent support, to Johnson’s 8 percent.

Several Sanders supporters said they would back Stein’s candidacy as an alternative, pledging “Never Hillary.” Julie Tyler, an independent contractor for Toyota in Los Angeles, said it won’t be Stein’s fault if the votes she draws hand the election to Trump.

“It will be the Democratic Party’s fault for picking a bad candidate,” she said.

But others were more cautious about abandoning the Democrats, even though their candidate didn’t end up as the standard-bearer. They said Clinton must convince them over the next three months that she believes in the platform that arose from negotiations with the Sanders campaign and is prepared to carry out its mandates.

“I’m a Democrat, but the Democrats have seriously underestimated the ire of their own voters,” said Christopher Fury, a Virginia delegate. He said that he won’t organize for Clinton, but that she still has time to win his vote. “Nobody that I know likes Donald Trump. Some people, however, are willing to let it burn a bit, and I mean b-u-r-n, not b-e-r-n.”

Ruth Ross, another Sanders supporter in the Virginia delegation, said that Stein’s platform is attractive to her but that she fears that “a vote for her would risk a Trump presidency.” And that outcome, said Martha Allen, a New Hampshire delegate, would undermine Sanders’s influence in the Senate, which none of his supporters should want.