Fans of Michael Moore may be loathe to admit it, even to themselves, but the slovenly director has given us a movie that serves as an unwelcome reminder of just how low the tone of political discourse in this country has sunk.

I'm speaking, of course, of "Fahrenheit 9/11," a thinly disguised campaign commercial masquerading as a documentary. It's not enough, apparently, for Moore to air his disagreements with President Bush's foreign policy. No, he must portray the commander-in-chief as a man who will wage a bogus war, and deliberately subject Americans to harm, to enrich himself and his rich pals who run the oil industries. Bush is not just wrong, you see. He's evil.

So intent is Moore on flinging mud that he doesn't seem to notice the underlying contradictions in his account. As a result, the president is somehow both a bumbling idiot and a wicked genius.

Now, if this viewpoint were confined only to a few observers on the fringe left, there wouldn't be much to complain about. Although Moore is popular among the denizens of the hard left, few serious elected officials, commentators or interest groups take him seriously. But in an alarming trend, the sort of rhetoric he traffics in has infiltrated leading organizations of the left, leading leftist commentators and leading liberals in Congress.

To see this trend in action, take an issue such as the environment.

According to the Environmental Protection Agency, the overall quality of our air has improved steadily on President Bush's watch. Specifically, concentrations of carbon monoxide have fallen by 15.5 percent, lead by 31.5 percent, nitrogen dioxide by 5 percent, sulfur dioxide by 11 percent, and particulate matter by more than 4 percent. The two pollutants that contribute to ozone formation, moreover, are at their lowest levels since 1970.

President Bush has advanced regulatory proposals to allow outmoded power plants, oil refineries and other industrial facilities to modernize, and thereby cut their emissions of harmful pollutants, and to require the overseers of our national forests to use proven forest management techniques to limit the number and extent of the devastating fires that have ravaged millions of acres of forest in recent years.

President Bush also has implemented the first-ever snowmobile emission standards, which would have the same effect as taking 30 million cars off the road. In May, his administration tackled pollution from heavy construction equipment by approving a rule that will reduce the pollution from sulfur in diesel fuel by 99 percent.

As an impressive environmental record, that's not bad, right?

Au contraire. The League of Conservation Voters reviewed this record and concluded that President Bush "is well on his way to compiling the worst environmental record in the history of our nation." Democratic presidential candidate John Kerry concurred, assessing these actions as "Abysmal. Worst record in modern history."

Sadly, overheated denunciations from liberals that imply evil intent on the part of the conservative politician who dares take a principled stand on an issue have become commonplace. These denunciations leave no room for nuance or debate, often linking crass or criminal motivations to the position being reviled. Thus, Sen. Ted Kennedy, D-Mass., alleges the war in Iraq "was made up in Texas" because it "was going to be good politically" and amounts to nothing more than a "fraud."

Sen. Tim Johnson, D-S.D., describes Republicans who support President Bush's approach to the War on Terror as the "Taliban wing" of the GOP. Hitler analogies have become increasingly popular. The anti-Bush entity Moveon.org, has featured ads likening President Bush to Adolf Hitler. Federal 2nd Circuit Court of Appeals Judge Guido Calabresi recently compared President Bush's election victory to the rise of Hitler and Italy's fascist leader Benito Mussolini.

Liberals who dissent from conservative policies seize on the most extreme forms of criticism to denigrate those policies and their advocates. Speaking in May at New York University, former Vice President Al Gore said President Bush "has created more anger and righteous indignation against us as Americans than any leader of our country in the 228 years of our existence as a nation." New York Times columnist Paul Krugman labels Attorney General John Ashcroft the "worst attorney general in history." Sen. Kerry likewise routinely excoriates Bush's foreign policy as "the most arrogant, inept, reckless, ideological foreign policy in the modern history of this country."

Sometimes liberals launch their critiques of conservative policy initiatives before the policy in question has even taken effect. Thus, Senate Minority Leader Tom Daschle declared the new Medicare prescription drug discount cards, one of the few market-oriented reforms included in last year's expansion of Medicare, a failure within 24 hours of their arrival, saying: "Seniors overwhelmingly now have rejected the drug discount card and this program."

Harsh and unequivocal criticisms that offer no grounds for negotiation or debate have become so commonplace in Congress that the traditional mechanism used to restrain improper language and characterizations used during floor debates -- the "taking down" or expunging of intemperate phrases or words from the official transcript of the debates -- is ignored. About two weeks ago, during a heated moment as the House considered the Defense Department's budget, one Democratic member described his Republican colleagues with whom he vehemently disagreed as "sleazy" and "the most cowardly Americans."

But rather than halt the debate and make the traditional parliamentary motion to have these words "taken down," the Republican to whom these words were addressed simply noted: "I know that words have been taken down for a lot less than that, and I think that that kind of language does not have any place on the floor of the House."

This Republican member was correct. Such words should be expunged from serious policy debates precisely because using them shuts down those debates. Faced with accusations such as those described above, what serious person would respond in a manner designed to enlighten or persuade? And who would listen to such a critique in the spirit of one who might actually be persuaded to their opponent's point of view?

Inevitably, shouting matches ensue. Partisans on both sides burrow in and tune one another out. And Red America grows redder, while its Blue America counterpart becomes ever more blue.

Michael G. Franc is vice president for government relations at The Heritage Foundation (heritage.org).