Joan Baez watched the mayor of Charleston, South Carolina, work himself to the point of tears. "She is going to sing not just a song, she is going to sing ... the song," John Tecklenburg declared from a makeshift stage in a downtown park. "This is a lady who's not just talked the talk and sang the songs of our life, but she has ..." and he kept on rhapsodizing until he got out of breath. "She was there in 1963, and she is here with us today ... Joan Baez!"

Baez hugged him on the way to the microphone, where she said, "I told him that was pretty good for a white guy." At 77, she can't help letting a little air out of most attempts to glorify her. And yet here she was, doing again what is the essence of her legend: showing up where the action is, with a song and a faith that a song can make a difference.

The occasion was a rally to mark the third anniversary of the massacre at nearby Emanuel African Methodist Episcopal Church, where a white man killed nine African-American congregants during a Bible study. Baez had come from Paris — taking a break from her worldwide farewell tour, the last sustained series of concerts of her nearly six-decade career. The song she would perform is called "The President Sang Amazing Grace," and it recounts how President Barack Obama spoke — and sang — at the funeral of the Rev. Clementa C. Pinckney, the church's slain pastor. Zoe Mulford, an obscure folk singer three decades younger than Baez, wrote the piece. But Baez — who has been lifting up others' songs since she championed the first protest visions of a scruffy waif named Bob Dylan — recorded the version that got people's attention.

Mulford was in the audience at the rally, slightly dazzled. "I heard Joan's voice for the first time in music class when I was 8 years old," she told me. "I was listening to her music when I was in my 20s and picking up a guitar and deciding what I wanted to sound like. She has been one of my heroes."

Baez strapped on a borrowed guitar. Her voice, an increasingly fragile instrument, felt tight from jet lag, she told me later. In the minutes before going onstage, she had tried loosening the voice and practicing on the unfamiliar guitar, but she wasn't satisfied. Masking her doubts behind a bright smile, she announced the song. "It's the story of the day that the president came to try and console people," she said. "The words were not enough. So he sang instead."

As she fingerpicked the opening lick, I wondered how a simple song could live up to the emotions of the event — grief, loss, hope. Local performers today had brought their beats and loops, their soundtracks and videos. And here was Baez with only a guitar. She sang a little huskily at first:

"A young man came to a house of prayer

"They did not ask what brought him there

"He was not friend, he was not kin

"But they opened the door and let him in"

Many in the crowd were standing, staring intently as they took in the words. After three verses came the chorus, the voice strong now:

"But no words could say what must be said

"For all the living and the dead

"So on that day and in that place The president sang 'Amazing Grace'

"The president sang 'Amazing Grace'"

When she finished, the crowd whooped and cheered. "It really touched my heart," said Roberta Williams, 60, a substance-abuse specialist. "It was just that effect it had — the performance, the atmosphere, the cause." Williams was accompanied by her daughter, Kris Bennett, 24; the mother had been stunned to learn that the millennial knew who Joan Baez was.

Bennett, who works at Z93 Jamz radio in Charleston and hosts a YouTube series on local hip-hop, told me she started following Baez on Instagram when she noticed the singer being tagged in videos posted by younger activists since President Trump was elected. She sees in Baez an elder who, in contrast to some, "is like, I understand you guys, I'm willing to help." Of Baez's performance that day, she said, "The song was really appropriate for everything that's happening right now. I think we're at this point where enough is enough, and seeing someone from the civil rights movement, a white woman who actually stands, that's a big thing." Bennett, who is black, added, "White silence is worse than agreeing with it. If you're not using your platform and your voice to say anything, then you're not better than the people who are doing horrible things."

Afterward, Baez walked to the church, where she met some family members of those who were murdered. She told the story of singing "Swing Low, Sweet Chariot" for the Rev. Martin Luther King Jr. in Grenada, Mississippi, in 1966, where she joined him in escorting black children to a newly integrated school. In the church, she reprised "Swing Low," amending the last line to refer to Trump: "Comin' for to carry me, you, us, even Donald, home."

"I have to put that line in about a man who really represents evil to me," she said to the group. "I don't believe a person is evil, or is born evil, but you certainly can crank out some evil deeds. What I'm impressed with here is that where there could have been resentment and nastiness, there's been acceptance, and where there could have been real hatred, there's been love. ... It's up to us to double our efforts in that way."

Baez's visit to Charleston lasted several hours, and after it was over, I realized that the whole affair, from the rally to the church, had been one long performance — a sincere one. It was Joan Baez playing Joan Baez, the woman being the legend; and somehow — after incalculable changes to the music industry, the splintering of social movements, the dislodging of protest anthems from their central role in activist culture — that still mattered.

"I feel a sense of responsibility that I am leaving," she says of her imminent retirement from the road. "At this point in history, me and my stuff are needed." She is taking this time to see if there is a new way to carry on being the public Joan Baez. That will be welcome news to her fans, because even as her voice — a once-soaring tone of soul and steel — is no longer capable of performing the way it used to, she signifies ideals many people want to hold on to: an independent approach to music, an insistence on political engagement, an irony-free safe space for harboring the hope, sometimes against strong evidence, that all is not lost.

Her last tour

Baez lives in a rambling yellow house in the hills above Palo Alto, California, with an affectionate, blind, blond bouvier des Flandres named Ginger. When Ginger lost the sight in her second eye a year ago, she used her other senses to map the couple of acres of property. Baez has been adapting similarly with her peerless soprano as it has deepened. Working with a vocal therapist, she has found a different way to do many of the old songs, while selecting new pieces that profit from her lower range. The work has extended the life of her singing. Still, the daily challenge of keeping her voice up to her own high standards is the main reason she plans to cease touring after the current run ends next year.

"If I could sing easily, I'd go on doing it, because I love it," Baez told me one afternoon over salad and ice cream at a wooden table in her kitchen. She speaks in a soft voice and laughs a lot. "But I don't like to see it deteriorate. ... It's deceptive, because the concerts are fantastic."

"Every song has to be re-crafted; everything has to be reinvented," she continued. "And that's the part that's tiring. . . . I'm not trying to get the achingly pure soprano. I just want to pop up to that note and know I can hang on to it for like a quarter of a second and then come back down - and even that is getting beyond my reach."

In her autobiography, Baez called her voice "my greatest gift, given to me by forces which confound genetics, environment, race, or ambition." But now, she said, "it's another voice. I like it. I like the sound of it. ... I'm clever enough to reinvent it in a way that people are going to want to hear it."

She's been forced to set aside some of her most iconic songs, though. The former president may be able to, but Baez can no longer sing "Amazing Grace." Nor Dylan's "Forever Young," one of the most requested in her repertoire, which she dedicated to Barack and Michelle Obama during the Peace Ball after the inauguration in 2009.

"In 'Forever Young' you get to that note that sustains, and that's what I can't do," she says. Other melodies can be tweaked, such as "Joe Hill," the union organizing song that she sang at Woodstock: "The last note on that used to be high and wonderful, and now it's — I'm okay with that. And jumping around in something like 'House of the Rising Sun' — this is what takes the work. Everything has to be in order. The body has to be in order, the breathing, the throat, everything, to get happily to those notes. And I can still do that. A lot of it is cellular memory. Songs that have cellular memory somehow are easier to get up there and actually hang out for a minute. But it's absolutely exhausting."

Her new album, "Whistle Down the Wind," with songs by Mary Chapin Carpenter, Tom Waits and others, is a meditation on enduring - defiant and wistful. The title of the last song is "I Wish the Wars Were All Over." Clearly they are not. And on the civil rights front, the Black Lives Matter movement reveals that race relations are, as Baez says, "in some ways worse than they've ever been."

I wondered if after nearly 60 years of working on those issues in action and song she's disappointed that we, as a society, have not come further. She cited a column she had recently read in The Washington Post by Karen Attiah, with the headline: "I no longer have hope in white America." The idea is that when there is no hope, there is still "the shadow of hope."

"I live in 'the shadow of hope,'" Baez said. "In 'the shadow of hope' ... you still do everything you can to make this a decent world. And that's how I feel. I don't know if it's now more than ever, but we're facing a total lack of empathy, cruelty, evil, and how do we face that in some way that we have a chance of at least preserving our own moral compass?"

Baez in Connecticut

Joan Baez is playing a sold-out concert at 8 p.m. Wednesday at the Shubert in New Haven.