In the middle of the 2000 presidential campaign, Vice President Al Gore was worried. He was trailing George W. Bush in the polls, and he was looking to define his candidacy in a big way. His idea was to deliver a major speech on global warming. There was probably no other issue he knew as well and felt as deeply about. As a Harvard undergraduate he had studied with Roger Revelle, one of the first people in the world to monitor carbon dioxide in the atmosphere and to predict that the increasing human-produced emissions would lead to disruptive climate change. After being elected to Congress in 1976, Gore had held the first Congressional hearings on global warming. And in 1992 he had written Earth in the Balance, a passionate, fact-flooded bestseller that detailed the dangers of global warming. “We must make the rescue of the environment the central organizing principle for civilization,” he proclaimed in that book. So a speech in which he would declare global warming the top priority of a Gore presidency would be in sync with his past and his soul. It would be highly authentic.

But his campaign consultants were not keen on turning global warming into the organizing principle of Gore’s presidential bid. As political journalist Joe Klein points out in his recent book, Politics Lost, their advice to Gore was simple: Don’t do it. Global warming did not poll as a top concern for voters, and anyone who cared about it was already with him.

Gore proceeded with the speech. But his staffers did nothing to highlight it, and the address barely registered. Gore’s concern for this serious matter was deemed inconvenient by the people he’d hired to win him the election. What he cared about most was marginalized by his own campaign–and he didn’t protest.

This episode is worth recalling as Gore throws himself into another campaign: to promote his new film, An Inconvenient Truth–a crisply directed documentary by Davis Guggenheim (who has directed episodes of 24 and Alias) that follows the self-described “recovering politician” as he travels the United States, and the world, presenting a slide show that vividly depicts the reality and perils of global warming. Just before Gore was to jet off to Cannes to screen the movie, he spoke with me and my first question was about that 2000 campaign incident. In the film, he notes that the good news is that because global warming is a human-induced crisis, it can be addressed by humans. But the humans who would have to do that are politicians. If Gore–with all his commitment to the issue–was not willing to campaign as a global warming warrior, how can he expect other politicians to take on this hard task?

Gore declined to rehash his 2000 decisions or to explain why it took losing an election (with an asterisk) to unleash the crusader in him. He only obliquely addressed the matter: “Here’s the underlying reality…. America is still in what someone described as a Category 5 denial on the seriousness of the global warming crisis. Until the American people change their minds about this reality, then the politicians in both parties are going to find rough sledding when they propose the serious solutions that are needed.” That is, an America in denial is a tough audience for a politician obsessed–healthily–with global warming. After the disappointing finale of the 2000 race, Gore said, he decided he “was going to do everything I could to change that underlying reality and to take this message to as many people as I could.” His mission, in a way, is to make the world safe for the politician that Gore might have wanted to be but was not. Hence, the traveling slide show–which he had first developed years earlier and which he says he’s presented about 1,000 times.

The show–and the film about the show–is engaging, as Gore displays charts, graphs, photos and video footage, mixing in wit and self-deprecating humor. One harrowing segment features computer simulations of New York, Beijing and other cities flooded by rising sea levels, caused by the melting of the polar ice caps. In the documentary Gore comes across as a master of the science, a committed and caring policy wonk, an engaging teacher and, yes, personable. He seems completely at home. It’s Al Gore at his best. (Everyone can use a good director.) And any Democratic voter who watches the movie will have the same reaction: Where was this Al Gore when we needed him? Why, I asked him, did the nation not experience that Gore in 2000? “When you are seen through the filter of a national political campaign,” he replied, “with your opponents offering caricatures every hour on the hour and a properly skeptical press corps”–he laughs a bit awkwardly–“assigning motives to every utterance and voters themselves saying, ‘Aha! I know why he’s saying that–he’s trying to get my vote,’ that is fundamentally different from the way it’s possible to see someone who is not in that context.”

Blaming the media is easy. But perhaps it’s too much to expect Gore to engage in self-flagellation when he is flogging a movie and riding a wave of positive publicity. In the movie he candidly refers to his decades-long efforts to turn global warming into a hot-button issue, remarking, “I feel as if I have failed to get this message across.” He’s doing what he can now. But when he looks at the Democratic Party leaders these days, he doesn’t find many compatriots. Congressional Democrats have proposed an energy-independence plan, but they’re hardly making planetary rescue a front-burner issue. (And Gore notes in the film that the window of opportunity for preventing climate catastrophe may close in a matter of years.) In fact, with an electoral strategy based partly on a backlash caused by rising gas prices, the Democrats are reinforcing the popular notion that Americans have a sacred right to cheap gas. Is Hillary Clinton, I asked, as committed as she should be? Gore didn’t take the bait, but he did say that the Democrats were not doing enough: “It gets back to that underlying reality. The country as a whole is not yet in a place where politicians feel comfortable.”

For all his doom and gloom in the film–it’s enough to give the most ardent enviro stomach pains–Gore told me he believes public opinion is near a tipping point. “Six months from now,” he said, “if we have this conversation, you and I will agree that the period between the spring and the beginning of winter was a period when the country changed dramatically on global warming.” What’s the reason for this green bullishness? His film? Gore ticked off the positive signs: Evangelical ministers have pronounced global warming a moral issue; corporate execs at General Electric, Du Pont and other companies have championed emissions-cutting measures as good for business; cities and towns have taken their own steps and called on the federal government to move; Mother Nature has kicked up more extreme weather (a true warning sign); and insurance companies around the world are beginning to worry. “Now, I have felt in times past that we were close to a tipping point, and I’ve been wrong,” Gore added. “I don’t think I am wrong this time.”

The Al Gore freed from electoral politics is far more appealing (see his recent Saturday Night Live appearance) and outspoken. In 2002 he fiercely criticized Bush for heading toward war in Iraq, and earlier this year he slammed the President for placing the Constitution in “grave danger” by insisting he had the inherent authority to eavesdrop on and imprison Americans without warrants. And Gore has renewed his career as an evangelist for ecological sanity without seeking attention for this work. (He didn’t approach the filmmakers–they came to him–and initially he was skeptical about the project.) As the documentary shows, he performs his new role with a panache and dedication that candidate Gore never conveyed. The good reviews have prompted speculation about another Gore presidential bid (despite a recent poll that shows his positive rating at a low 28 percent).

“I have no intention of being a candidate,” he said before catching that flight to Cannes. He sounds as if he might mean it. But let’s put the question slightly differently: Does he believe that a politician who showed a slide show like his would have a chance as a presidential candidate? “The role of global warming in American politics,” he answerd, “will change when the minds of the American people change about the urgency of the issue. And that is why I made this movie–to change the minds of the American people.” That’s a tall order–perhaps taller than winning the White House–but one that seems to come more naturally to him than campaigning.

“I have become very impatient,” Gore wrote in Earth in the Balance, “with my own tendency to put a finger to the political winds and proceed cautiously.” But now he has no consultants telling him what to do to win an election. He is simply trying to save the world–literally–by following his own instincts. The pity is, he’s probably right that this is a job for a former politician, not a current one.