Advocates of the market-based cap-and-trade approach to curbing carbon dioxide appeared to make headway early in Obama's first term with a hard-fought measure that passed the House. But some environmentalists were rankled by the compromises, and the green movement never united behind the bill. Meanwhile industry opponents launched a ferocious and well-funded campaign to kill it. Obama, battling economic crisis from his first hours in office, spent much of his political capital pushing through his health-care initiative while climate action died a slow death in the Senate. (See related story: "California Tackles Climate Change, But Will Others Follow?")

At the start of Obama's second term, though, Al Gore's favorite sound bite—that political will is a renewable resource—may have some validity.