When Al Gore won the Nobel Peace Prize on Friday, conservatives reacted with apoplexy. Talk show hosts such as Rush Limbaugh, conservative bloggers and other Republican faithful denounced the prize as a fraud.

You might wonder why they care so much — Gore, after all, obviously is not going to run for president, and even some conservatives concede that global warming is real. The answer is that Gore's triumph is a measure of George W. Bush's disrepute.

Indeed, in the political culture, Gore's role is as a negative indicator of the president's standing. For all the talk of a "new Al Gore," there's nothing new about the man. His public reputation is almost entirely a function of Bush's.

The high point of Bush's prestige came in the months after Sept. 11, 2001. As Bush put it in a year-end interview: "All in all, it's been a fabulous year for Laura and me." (It certainly was, if you could put aside the 3,000 American deaths, which Bush apparently could.)

That was also the moment when it was most fashionable to ridicule Gore. He was described as "goofily bearded" or "sulking." Democrats were publicly declaring they were glad Bush, and not Gore, was in the Oval Office.

Gore, the thinking went, was too intellectual and lacked Bush's gut-sense understanding of good and evil. A staunch Gore backer explained his relief at Bush's victory thusly: "(Gore) may know too much." At the time, this trait was seen as far more problematic than knowing too little. A poll in late 2001 found that 76 percent of Americans preferred Bush over Gore as a war leader.

In 2002, when Gore began to criticize Bush's approach to Iraq, conservatives attacked him savagely. The popular phrase at the time was "moral clarity," a trait Bush had but Gore lacked.

It's not an accident that the current celebrations of Gore come at a time when Bush's popularity has cratered. Once conservatives mocked Gore as the radical tribune of a tiny political fringe; now it is they who represent the fringe.

Their argument with Gore over global warming is a telling indicator of their weakened position. Suddenly, open debate looks better than absolute clarity. Steven F. Hayward, a global warming skeptic at the conservative American Enterprise Institute, sniffed: "The Nobel will be one more quiver in Gore's arsenal of intransigent moral authority by which he refuses to debate any aspect of the subject and declares the entire matter 'settled.' It's never a good sign when politicians declare a scientific matter settled; we all remember how well that worked out for the Vatican when they told Galileo 400 years ago that astronomy was settled."

So Gore can't declare that any scientific matter is settled? (What about the Earth revolves around the sun — would that offend conservatives?) Funny what happens when it's your views that are out of the mainstream.

The defensiveness of Gore's critics comes because he is the ultimate rebuke to Bush. Gore, obviously, is the great historic counter-factual, the man who would have been president if Florida had a functioning ballot system. More than that, he is the anti-Bush. He is intellectual and introverted, while Bush is simplistic and backslapping.

Some of us prefer a president like Gore no matter what. But many people don't have a strong preference, or don't think very hard about what Gore would have been like as president. Therefore, he lacks a positive identity; people think of him only as the anti-Bush.

But Gore is highly prescient in his own right. Not only was he an early activist against global warming, he favored the first gulf war , urged military action in the Balkans and opposed the current Iraq war. His denunciation of Bush as a captive of business interests — ridiculed as dime-store populism — has proved a telling critique of this administration, which has crafted legislation perfectly suited to oil companies, HMOs and pharmaceuticals. But his standing in history will probably have less to do with anything he said or did than with Bush's record. Fortunately for Gore, although unfortunately for the world, he's likely to make out just as well either way.

Jonathan Chait writes the TRB column for the New Republic. he wrote this commentary for the Los Angeles Times.