MIAMI — The guest of honor strolled across the stage — hair slicked back and grayed, no tie — embracing his host, briefly, before looking out on the campaign crowd.
It had been a while. He opened with something safe.
“I understand you’ve got a pretty good women’s volleyball team here,” he said, a bit tepidly, inside a college gymnasium on Tuesday. “So go, Lady Sharks. Is that what you say?”
Al Gore was back.
In a rare return to presidential politics, Mr. Gore, who was Bill Clinton’s vice president, joined Hillary Clinton for a 45-minute Democratic call to arms, vacillating between a familiar drawling delivery and the urgency of a seer sent from another era to warn future generations of prospective doom.
“Your vote really, really, really counts,” he said, in the state synonymous with his excruciating 2000 election loss. “You can consider me as an Exhibit A.”
It was a remarkable turn in one of the most consequential, and fraught, relationships in recent Democratic political history — a halting public embrace between two figures long defined by rivalry, ambition and a complicated union with the same man.
The event’s ostensible focus was climate change, Mr. Gore’s signature issue. But the wider message of the gathering, 16 years after the recount fight that begot the presidency of George W. Bush, was unsubtle: As Mrs. Clinton seeks to encourage registration efforts and convince Americans that every ballot counts, Mr. Gore is the Democrats’ ambulatory cautionary tale.
“Now, for those of you who are younger than 25, you might not remember the election of 2000 and what happened here in Florida,” he said, addressing students from Miami-Dade College, among others in attendance. “For those of you older than 25, I heard you murmuring just now.”
Soon, a chant rang out: “You won!”
Introducing Mr. Gore, Mrs. Clinton spoke of clean energy, curbside gardens, the Paris climate agreement and Donald J. Trump’s suggestion that climate change is a hoax.
She commended Mr. Gore’s Nobel Peace Prize and his documentary, “An Inconvenient Truth,” presenting him as “our former vice president, the climate change leader and all-around great guy Al Gore.”
“There isn’t anybody who knows more, has done more, has worked harder,” she said. “I can’t wait to have Al Gore advising me when I am the president.”
He stepped to the microphone, hugging Mrs. Clinton as she smiled.
There was a time when these two shared the stage often as crowds waved signs with both of their surnames.
After Bill Clinton’s 1992 election, Mr. Gore and Mrs. Clinton quickly established themselves as rivals for Mr. Clinton’s ear — a pair of policy wonks seeking influence in a new administration.
It was their similarities, at least in part, that seemed to compel Mr. Clinton to choose Mr. Gore in the first place. “He reminds me of Hillary,” Mr. Clinton told a former top aide, Paul Begala, according to Mr. Begala. “When he gets hold of something, he never lets loose.”
Together with the vice president and his former wife, Tipper, the Clintons shared dinners and concerts, White House bowling outings and nights at Camp David.
Mr. Gore’s plans to succeed Mr. Clinton suffered, in part, from the president’s affair with Monica Lewinsky and the firestorm that followed. Tensions persisted as Mr. Gore sought to distance himself from his boss on the campaign trail, effectively sidelining Mr. Clinton as a surrogate, wounding the departing president.
“I understand the disappointment and anger that you feel toward President Clinton,” Mr. Gore told voters at a televised forum then, “and I’ve felt it myself.”
At the same time, Mrs. Clinton had set off to run for the United States Senate, competing for party resources and attention just as Mr. Gore was straining to step out of the Clintons’ long shadow.
She won. He lost.
In the years since, Mr. Gore declined to endorse Mrs. Clinton in the Democratic primary campaign during either of her presidential runs. He announced his support for her this year in late July, over Twitter. He did not attend the Democratic convention.
The rally on Tuesday dwelled little on this past, or the details of Mr. Gore’s defeat.
Hanging chads were not broached. Butterfly ballots were not invoked. Yet other Gore-era echoes have resounded through this heady campaign season.
Young voters, wary of the Democratic nominee, have weighed third-party options, delivering fresh nightmares of Ralph Nader’s 2000 campaign to bleary-eyed Democratic operatives.
The grim history of Mr. Clinton’s behavior with women has reassumed center stage, with Mr. Trump raising his infidelities as a campaign issue. (At least twice during Mrs. Clinton’s remarks on Tuesday, protesters ridiculed Mr. Clinton’s past. Mr. Gore stared straight ahead, his hands clasped.)
There is even a legal skirmish over voting regulations here, with Democratic officials successfully extending a registration deadline, against the wishes of the state’s Republican governor, because of a recent hurricane.
The speakers on Tuesday focused most intensely on this extreme weather and its consequences.
Mrs. Clinton cited the devastation in Florida and Haiti from Hurricane Matthew — “If you need additional convincing, just remember what happened this week,” she warned — and reminded voters of the protracted drought in California.
Mr. Gore, too, held forth on the cause of his postpolitical life, making his case as if reading from a slide show projection. He quoted Thomas Edison, warned of rising sea levels and lurched into a discussion of comparative solar energy commitments.
“Massachusetts installed more solar energy last year alone than Florida has installed in its entire history!” he said.
“Ridiculous!” someone yelled back.
“Yes, it’s ridiculous!” Mr. Gore said. “That’s exactly right.”
By then, some students had buried their heads in their phones.
But the former vice president ended with a flourish.
“Please take it from me,” he said. “Every. Single. Vote. Counts.”
“We love you, President Gore!” a woman shouted from the bleachers.
Moments later, Mr. Gore wrapped up, turning toward Mrs. Clinton for a brief negotiation as the room cheered.
“Wanna do a hands-up?” he asked, cupping her right hand in his left.
“Yeah!” Mrs. Clinton said.
One more time, their arms shot skyward.