As Hillary, Obama, and Edwards continue to slug it out in the early primary states, one name is conspicuously absent among the Democratic candidates to become the next president of the United States. Where is Al Gore? The man who received more votes than George W. Bush did in 2000, who served eight years as Bill Clinton’s vice president, and whose climate change evangelism has been rewarded with an Oscar and Nobel Peace Prize has resolutely refused to enter the race, even though he might well have won it.

Ever since the documentary An Inconvenient Truth catapulted Gore to international superstardom in 2006, countless citizens and opinion leaders at home and abroad have urged him to pursue the presidency. For its 2007 Person of the Year issue, Time magazine asked Gore if he did not have “a moral obligation” to run, given the unparalleled power of the White House and the urgency of the climate crisis. Gore gave much the same answer he has been giving for months now: although he had “not completely ruled out the possibility,” he did not expect to run for office; the best thing he could do to fight climate change was to stay focused on “changing public opinion.”

Pundits find it hard to believe that a lifelong politician could turn his back on the White House; some speculate that Gore is being coy, waiting to see if other candidates stumble. I doubt it. As someone who has covered Gore’s climate activism for 15 years now, since first interviewing him at the U.N. Earth Summit in 1992, I think he sincerely believes that changing public opinion is more important than changing presidents. What’s more, Gore has good reasons for this unconventional conclusion — reasons that deserve our attention, for they suggest the kind of battles that must be fought and won if catastrophic climate change is to be avoided.

I spent two hours one-on-one with Gore just before An Inconvenient Truth was released. Much of our interview focused on an irony that seems to have escaped many of those who have urged him to run for president: the last time Gore served in the White House, he failed to deliver much progress against global warming. During its eight years in office, the Clinton-Gore administration did not pass a single major law against climate change. It did sign the Kyoto Protocol, but only after watering it down with crippling loopholes, and then it chose not to seek Senate ratification of the treaty.

In our interview, Gore acknowledged these failings. But he argued that the blame lay not with him or Clinton, who, he said, “was much more responsive than not.” Rather, Gore said, “the resistance was tremendous” from the status quo. The two richest, most powerful industries in American history, oil and autos, were fiercely opposed to cutting emissions, as were coal and electricity companies. Kyoto was “blocked by pressure from the polluters,” Gore told me, adding that ExxonMobil and other big companies “purposely confused people” with tens of millions of dollars of advertising and lobbying that misrepresented and disparaged the science behind global warming. This disinformation campaign encouraged “massive denial in the country as a whole” and “conditioned the battlefield” in Washington so that Congress ended up blocking reform.

The lesson Gore seems to have drawn from his defeats in the White House is that being president is not enough to create real change, especially if powerful interests are against you. The only way to defeat them is to recondition the battlefield — to build such a pervasive wave of public pressure that no matter which politicians get elected, each will feel compelled to take action, even if it means disappointing ExxonMobil and friends. As Gore told Time, the climate crisis “requires a fundamental shift in public opinion at the grassroots level to embolden members of the legislative branch to take action.”

A case in point: In December, for the first time, a Senate committee passed a major climate change bill. Many environmentalists cheered the Warner-Lieberman bill, which promised to cut greenhouse-gas emissions 70 percent by 2050. But the bill’s provisions, especially one giving polluters free pollution permits, suggest that it will deliver much smaller emissions cuts than advertised. Corporate influence, it seems, remains plenty strong on Capitol Hill. Gore called the bill, which the full Senate will soon consider, “not sufficient.” He urges more radical action, including a ban on new coal-fired power plants. He has even encouraged young people to blockade the bulldozers attempting to build coal plants.

The three leading Democratic presidential candidates all understand the climate issue well and promise to do big things to address it. So, to a lesser extent, do Republicans John McCain and Mike Huckabee. But if any of them succeed as president in reversing Bush’s disastrous climate policies, he or she will owe Gore an enormous debt. Gore’s years in the White House appear to have taught him a vital lesson about modern democracy, a lesson that is omitted from most textbooks and news coverage: being president, like being right, is not enough. The only way to beat organized money is with organized people, lots of them. Gore is now helping to build that grassroots pressure, even though it means giving up on the presidential dream he has harbored since childhood. His is an act of vision and sacrifice, one for which all of us should be grateful.