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.”