Al Gore once cherished the illusion that he and his future wife “Tipper” were prototypes for the romantic couple in Erich Segal’s novel Love Story. When the author begged to demur, Gore was left with egg all over his face.

This public humiliation seems emblematic of Gore’s life. The mantle of the most powerful man in the world might have descended on Vice-President Gore’s shoulders in 1998 if Bill Clinton had been forced to resign over the Monica Lewinsky affair. But “Slick Willy” wriggled out of it.

Even Gore’s best jokes seemed to backfire. In a quip about his perceived woodenness he said: “They opened up my leg and found termites.” It merely set up a New York comic’s gag that Clinton’s dog, Buddy, mistook him for a tree.

In 2000 Gore could have beaten George W Bush to the presidency, only to have the job wrenched from his grasp by a questionable margin and a capricious Supreme Court. His fellow Democrats damned “Gore the Bore” for losing and accepting defeat too graciously. Retiring into a sort of Nixonian exile, he was seen as a figure of scorn and pity.

Now Gore, 58, is back, miraculously transformed into a bulked-up Clark Kent figure greeted rapturously at the forefront of America’s ecological awakening. At Cannes last week he launched his global warming documentary An Inconvenient Truth with a panache that upstaged Hollywood stars.

If Tom Hanks opted for coyness, Gore made the grand entrance, bowling over journalists with a passion and fluent charm that he manifestly lacked six years ago. Asked how he would like to be addressed, he replied smoothly: “Your Adequacy.”

His sleek hair was greyer and for a tall man he looked even bigger. Reports that he had become self-conscious about his weight were countered by an interviewer’s observation: “It looked like solid muscle to me.” This week he brings his message to Britain.

Positive reaction to the film, recording his personal credo on the “planetary emergency”, has started a buzz among Democrats on whether Gore will run again in 2008. To those who harbour doubts about the polarising effect of their frontrunner, Hillary Clinton, it seems like a good idea.

In Gore’s camp there is a feeling of unfinished business with the Clintons. A “friend” was quoted last week as saying: “If Clinton hadn’t been impeached, Al Gore would be president and the world would be a different place.” Clinton’s side retorts that if Gore had run even a half-decent campaign he would have won.

The two men were said to be no longer on speaking terms when they left the White House but they have evidently made up. “We’ve just been through too much together,” Gore said recently. “We have a bond that’ll never be shaken.”

However, a former Gore adjutant told New York magazine last week that Gore’s relations with Hillary are not so harmonious. “He intensely dislikes her. It all goes back to 1993 and 1994, when there were two vice-presidents: Al Gore and Hillary Clinton. They fought for turf, for resources, for projects. It was like a sibling rivalry over who was the second-most important person in the White House.”

The Gore 2008 bandwagon is gathering momentum. He has important backers in Hollywood, Silicon Valley and New York. In Washington, where only one congressman has called openly for Gore to run, there is more caution. The general tenor is that Gore was “god-awful” in 1988, a disaster in 2000 and would bomb again in 2008.

Yet Democrats desperately need to win and if Gore suddenly looks like a winner, he might get the ticket. As one of Bush’s most outspoken critics he has made searing indictments of the Iraq war, wiretapping and state-run torture.