Jill Stein, the Green Party’s serial presidential candidate, has heard the pleading from strangers.

“How does it feel to be personally responsible for actually bringing Donald Trump into power?” Ms. Stein recalled being asked this year by a man in New York — another heckler accusing Ms. Stein of tipping the 2016 election.

She has absorbed the glowering across her anxious blue neighborhood outside Boston.

“When people are being propagandized,” Ms. Stein said, “they won’t be especially friendly on the street, put it that way.”

And as she weighed another campaign this time, she found resistance in the most intimate constituency: her own family.

“For her political activities, she does not have the support of the family,” one of Ms. Stein’s adult sons said in an interview, asking not to be identified by name to avoid any personal or professional repercussions from associating with her. “When she told us she was going to run again back in October 2023, we asked her not to.”

Ms. Stein has ignored them all.

Now, strategists in both parties agree, her decision might well echo again through history — by helping a man whose values she nominally abhors.

Ms. Stein is back on the ballot almost everywhere that matters, returning to the campaign fore in an ostensible coin-flip race between Mr. Trump and Vice President Kamala Harris. Democrats see Ms. Stein’s bid as a direct threat in a year when even relatively small voter pools might carry near-existential stakes.

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