In offices in State Line, Pa., an intense, bespectacled man tirelessly recounts how the 1911 Catholic Encyclopedia "predicts the anti-Christ will come from Jewry" and warns of the Jews' role in the coming "New World Order."

At a gathering near the Philadelphia airport, men in priests' collars and brown monks' robes rage against the "Judeo-Masonic" conspiracy to destroy the Catholic Church, the "Marxist-Jewish" scheme to wreck American schools, and even an elaborate 9/11 plot, "predicted by the Blessed Virgin Mary 84 years ago."

For most Americans, the world of "radical traditionalist Catholicism" is so remote and little-known -- it entered the nation's consciousness, just barely, with revelations about the strident anti-Semitism of actor Mel Gibson and his father, Hutton -- that it may seem wholly irrelevant to the modern world. Is it really important what a group of people, many excommunicated and most gathered behind the walls of their monasteries and other institutions, think about the Jews? That many believe there was no Holocaust? That some say every pope since 1958 has been illegitimate, and a few even insist the real pope has been kidnapped?

The fact is, it does matter. As explained in a remarkable and sweeping story by the Intelligence Report's Heidi Beirich, the best estimates suggest there are 100,000 radical traditionalists in America, a number that appears to be growing. And while the size of this movement is dwarfed by the 70 million mainstream Catholics in this country, these energetic men and women are having an influence.

For one thing, the open anti-Semitism that characterizes the movement is leaking into other subcultures, some of them especially dangerous.

Last September, Father Nicholas Gruner, leader of the International Fatima Rosary Crusade and a key player in the radical traditionalist milieu, celebrated a special morning Mass at the Washington, D.C., conference of The Barnes Review, a Holocaust denial journal, also attended by neo-Nazis and other white supremacists. In February 2006, John Sharpe, head of the Legion of St. Louis and another leading radical traditionalist, sold books at a conference of the racist magazine American Renaissance that also played host to neo-Nazi David Duke. (Last December, Duke spoke to a Holocaust denial conference hosted by the Iranian government.)

In one case, the simmering anti-Semitism of the radical traditionalists may even have affected the thinking of a serial-killing terrorist. A new book by Maryanne Vollers, Lone Wolf: Eric Rudolph: Murder, Myth, and the Pursuit of an American Outlaw, suggests that Rudolph may have been influenced by radical traditionalism, in addition to his known ties to the neo-Nazi theology of Christian Identity.

The movement also may be gaining influence on the larger political scene. A case in point is that of Christopher Ferrara, leader of the American Catholic Lawyers Association. Ferrara, who writes for the anti-Semitic, radical traditionalist journal The Remnant, was the lawyer for the family of Terri Schiavo and a key player, along with Republican and Christian Right leaders, in getting Congress to pass a law to keep the severely brain-damaged woman alive. It was later overturned.

In the United States, we are accustomed to thinking of race as the critical fault line splitting our society. But in the world at large, religion is just as divisive.

From Iraq to the former Yugoslavia to uncounted other regions, religiously based violence has recently torn apart societies that once included people of different faiths living together in peace. Even in the United States, with its strong tradition of religious pluralism, religious conflicts seem to be increasing almost yearly.