As Democrats have stepped up their explicitly religious appeals to Catholic voters, these bishops have pushed back against the intrusion on their turf. While Democrats talked of finding common ground on abortion, Archbishop Charles Chaput of Denver, the informal leader of this side of the American church, gave a much-publicized speech denouncing Obama as “the most committed abortion rights candidate in history.” Chaput chose to publish his remarks on the Web site of a think tank co-founded by George — the man who had himself argued in an essay disseminated widely last fall through conservative circles, Fox News and Christian radio that Barack Obama was “the most extreme pro-abortion candidate ever to seek” the presidency.

George’s role as an adviser to these bishops began more than 20 years ago, when he was a young professor and recent Ph.D. A mutual friend introduced him to the Rev. John Myers, then a bishop in Peoria, Ill., who was working on a pastoral letter about the moral obligations of Catholic voters and politicians. With George’s assistance, Myers wrote a letter laying out the case that abortion, as the taking of a life, was a crime against the natural law of human reason, not merely a violation of Catholic theology. Therefore, Myers and George argued, Catholic politicians and voters were wrong to write off the church’s teachings as a matter of personal faith. What’s more, the letter warned, voting for a candidate or a law upholding abortion rights would almost invariably put a Catholic so far outside church teachings that he should not receive communion. As the first systematic rebuttal to Mario Cuomo and other Catholic politicians who support abortion rights, the letter kicked off a now-familiar debate inside the church. “Whenever I venture out into the public square, I would almost invariably check it out with Robby first,” Myers, now the archbishop of Newark, told me. Many of the bishops, Myers says, rely on George as “a touchstone” and “the pre-eminent Catholic intellectual.”

Last spring, George was invited to address an audience that included many bishops at a conference in Washington. He told them with typical bluntness that they should stop talking so much about the many policy issues they have taken up in the name of social justice. They should concentrate their authority on “the moral social” issues like abortion, embryonic stem-cell research and same-sex marriage, where, he argued, the natural law and Gospel principles were clear. To be sure, he said, he had no objections to bishops' “making utter nuisances of themselves” about poverty and injustice, like the Old Testament prophets, as long as they did not advocate specific remedies. They should stop lobbying for detailed economic policies like progressive tax rates, higher minimum wage and, presumably, the expansion of health care — “matters of public policy upon which Gospel principles by themselves do not resolve differences of opinion among reasonable and well-informed people of good will,” as George put it.

A few months later, in a July 17 letter to Congress, the bishops did something close to that in the health care debate. Setting aside decades of calls for universal coverage, the bishops pledged to fight any bill that failed to block the use of federal subsidies for insurance covering abortion. “Stalin famously asked, ‘How many divisions has the pope?’ ” George wrote to me in an e-mail message after House Speaker Nancy Pelosi allowed a vote on an amendment that satisfied the bishops’ demands. “I guess Pelosi now knows.”

In the American culture wars, George wants to redraw the lines. It is the liberals, he argues, who are slaves to a faith-based “secularist orthodoxy” of “feminism, multiculturalism, gay liberationism and lifestyle liberalism.” Conservatives, in contrast, speak from the high ground of nonsectarian public reason. George is the leading voice for a group of Catholic scholars known as the new natural lawyers. He argues for the enforcement of a moral code as strictly traditional as that of a religious fundamentalist. What makes his natural law “new” is that it disavows dependence on divine revelation or biblical Scripture — or even history and anthropology. Instead, George rests his ethics on a foundation of “practical reason”: “invoking no authority beyond the authority of reason itself,” as he put it in one essay.

George’s admirers say he is revitalizing a strain of Catholic natural-law thinking that goes back to St. Thomas Aquinas. His scholarship has earned him accolades from religious and secular institutions alike. In one notable week two years ago, he received invitations to deliver prestigious lectures at the Southern Baptist Theological Seminary and Harvard Law School. His critics, including many of his fellow Catholic scholars, argue that he is turning the church into a tool of Republican Party. They say he is too focused on the mechanics of sex and morality, neglecting the other sides of the Christian message: the corruption of human reason through original sin, the need for forgiveness and charity and the chance for redemption. Citing George’s comparison of Catholic scholars who support abortion rights to defenders of chattel slavery, Cathleen Kaveny of the Notre Dame Law School, another scholar of law and theology in the Thomistic tradition, has called George and his allies “Rambo Catholics” and “ecclesiastical bullies.”

I met George 20 years ago, when I was a Prince­ton student and he was praying for tenure. The next time I saw him was in 2005, when he invited me back for a postelection conference on the future of the conservative movement. Rove spoke at lunch. To a movement still stinging from decades of condescension, George brings gleaming Ivory Tower credentials: degrees in law and theology from Harvard; a doctorate in philosophy of law from Oxford; a Supreme Court fellowship; and the endowed chair at Princeton that Woodrow Wilson once held.