The f-bomb of American politics is the word "fascist," routinely hurled by the left at conservatives. Ronald Reagan and Barry Goldwater were smeared as incipient fascists, and George W. Bush now receives the honor, along with practically anyone to the right of Rosie O'Donnell on a college campus.

The operational meaning of the word "fascism" for most liberals who invoke it is usually "shut up." It's meant to bludgeon conservatives into silence. But many on the left also genuinely believe that there is something fascistic in the DNA of contemporary conservatism, as if Republican Party conventions would get their rightful treatment only if they were worshipfully filmed by Leni Riefenstahl.

In his brilliant new book "Liberal Fascism," Jonah Goldberg (a colleague of mine) demonstrates how the opposite is the case, that fascism was a movement of the left and that liberal heroes like Woodrow Wilson and Franklin Delano Roosevelt were products of what Goldberg calls "the fascist moment" in America early in the 20th century. How we think of the ideological spectrum -- socialism to the left, fascism to the right -- should be forever changed.

Benito Mussolini was a socialist and earned the title "Il Duce" as the leader of the socialists in Italy. When he founded the fascist party, its program called for implementing a minimum wage, expropriating property from landowners, repealing titles of nobility, creating state-run secular schools and imposing a progressive tax rate. Mussolini took socialism and turned it in a more populist and militaristic direction, but remained a modernizing, secular man of the left.

The Nazis too were socialists, "enemies, deadly enemies, of today's capitalist economic system," in the words of the party's ideologist Gregor Strasser. The party's platform sounded a lot like that of the Italian fascists. The Nazis wanted to chase conventional Christianity from public life and overturn tradition, replacing them with an all-powerful state. Both Hitler and Mussolini were revolutionaries, bitterly opposed to "reactionary" forces in their societies.

By what standard, then, are they considered conservatives who took things to extremes? The left points to their anti-Semitism and militarism. But anti-Semitism isn't an inherently right-wing phenomenon -- Stalin's Russia was anti-Semitic. As for militarism, these regimes looked to it as a way to mobilize and organize society, something deeply anathema to the anti-statist tradition of postwar American conservatism.

On the other hand, the progressive movement of the early 20th century looked to Mussolini as an inspiration and shared intellectual roots with European fascism, including an appreciation of the "top-down socialism" of Otto von Bismarck. Goldberg eviscerates Woodrow Wilson as the closest we have ever had to a fascist president. Wilson and his supporters welcomed World War I as an opportunity to expand the state, instituting "war socialism" and a far-reaching crackdown on dissent.

FDR picked up where Wilson left off. The crisis of the Great Depression was the occasion for reviving "war socialism." The man who ran the National Recovery Administration was an open admirer of Mussolini, and the alphabet soup of New Deal agencies had their roots in World War I and the classic fascist impulse to mobilize society and put it on a war footing.

Goldberg sees the fascist exaltation of youth, glorification of violence, hatred of tradition and romance of "the street" in the New Left of the 1960s, still the subject of the fond memories for the liberal establishment in this country. Goldberg argues that "liberal fascism" -- the phrase was coined by H.G. Wells, and he meant it positively -- is a distant heir to European fascism. The liberal version is pacifist rather than militaristic and feminine rather than masculine in its orientation, but it also seeks to increase the power of the state and overcome tradition in sweeping crusades pursued with the moral fervor of war.

Goldberg's keen intellectual history is, at bottom, a profound cautionary tale about the perils of state aggrandizement and of revolutionary movements. If nothing else, it should convince liberals that it's time to find a new insult.