The presidential candidates made their first joint public appearance before an audience of 5000 parishioners at Rick Warren's Saddleback Church in Lake Forest, California on Saturday.

It's remarkable that Obama and McCain agreed to be quizzed about their faith by an evangelical pastor in his mega-church.

The event helped cement Rick Warren's status as one of the preeminent evangelical leaders of his generation.

So, who is Rick Warren and how did he get to be so influential?

I asked five experts on religion in America about the political significance of Warren and the Saddleback Civil Forum. A clear picture emerged from these discussions: Warren is at pains to present himself as an affable moderate who can work with Republicans or Democrats. Both parties want to curry favor with him because he speaks to a subset of moderate evangelicals who could tip the balance of power.

Warren has already built a 22,000-member congregation and a global network of influence by successfully marketing a consumer-centric evangelism to the suburban middle class. Now, Warren is marketing himself to America's political elite as a new breed of evangelical leader--someone who might be a more congenial ambassador to the evangelical base than older hardliners like James Dobson or John Hagee.

However, experts stress that the differences between Warren and the older evangelical leaders may be more stylistic than substantive.

"Warren's different from Dobson in that you're not going to hear him saying all this bitter nasty stuff about secularists or the pro-choice movement," says Sarah Posner, religion columnist at the American Prospect and author of the new book on the prosperity gospel, God's Profits.

Yet, Warren remains a hardliner on social issues like abortion, gay marriage, stem cell research, and euthanasia. As Posner points out, immediately after the candidates forum, Warren likened abortion to the holocaust--but, that while holocausts were deal-breakers for him personally, other people might feel differently about voting for a pro-choice candidate.

Warren wasn't always so easygoing.

Author and religion journalist Michelle Goldberg recalls a letter that Warren sent to his congregation before the 2004 election, informing them of their Christian duty to vote according to certain "non-debatable" social issues, notably abortion and gay marriage.

"It could have been written by James Dobson," she says.

"Warren is now putting forward a new image and a new style, but not new ideas or really new politics," Goldberg explains, "He's doing it at a time when it makes a lot of sense for an ambitious preacher with aspirations to power to stop putting all his eggs in the Republican basket

Warren has also set himself apart by taking an interest in issues like AIDS and poverty that have not traditionally been targets of evangelical fervor. Progressives may applaud Warren's concern about AIDS, but they probably won't like his proposed solutions. For example, Warren is a close ally of Ugandan pastor Martin Sempa who advocates sexual abstinence and faith healing as solutions to the AIDS epidemic.

Jeff Sharlet is the author of Killing the Buddha, a study of alternative religious communities in America, and The Family, a history of elite fundamentalism. He describes Warren as "perhaps the most influential public preacher since Billy Graham."

The secret to Warren's success is marketing.

"Warren is a pioneer of 'seeker sensitive' evangelicalism, aka consumer-tested Christianity. Saddleback is designed to seem like what its attendees want it to be," Sharlet says, "It's more mild-mannered than the mean old fundamentalism of the late Jerry Falwell, more 'life-style' oriented, a theology specially-made for its Orange County congregation: every bit as conservative as old Jerry's faith, but much more suburban, much more middle-class."

Warren does take as slightly softer line on the relationship between church and state than many in the evangelical old guard, according to journalist and religion blogger Sara Robinson. Even so, few progressives would regard Warren's position as moderate in any sense.

"He's very aggressively working to Christianize the world; but unlike [James Dobson, John Hagee, and Rod Parlsey], he doesn't seem to think that non-Christians deserve to be punished by their governments for their heresy," Robinson explains.  

Ultimately, both campaigns are looking to Warren because he speaks to a subset of moderate evangelical swing voters who could hold the balance of power in 2008.

"[T]he hard-core Religious Right - the Dobsonites, Hagee and Parsley and Robertson's folks - are somewhere between 8-10% of the electorate. Nobody expects them to ever do anything other than vote for Republicans. There's another group, perhaps another 10-15% of the electorate, who are more of a swing vote, even if they do share some or all of the political stances of the Religious Right," explains Pastor Dan Schultz, a United Church of Christ minister who blogs regularly about religion and politics at Street Prophets.

Schultz argues that many religious Democrats are eager to paint Warren centrist among religious voters. Schultz disputes that characterization, noting that most religious voters favor some kind of abortion rights, whereas Warren insists that fertilized ova have full human rights from the moment of conception.

"Like [Billy] Graham, [Warren] knows that liberals mistake his kind-spiritedness for moderation," says Sharlet, "In fact, Warren stands side-by-side with the hardest right-wing of fundamentalism, theological point by point. But he's a much better salesman."