You can call it the Trinity of the Religious Left. E.J. Dionne, Amy Sullivan and Jim Wallis are all out early this year with books celebrating the decline of the religious right.

The three come from different backgrounds — Dionne classifies himself as a liberal Catholic, and Time magazine’s Sullivan

and Sojourners magazine’s Wallis identify themselves as evangelicals. But they have drawn a similar conclusion: The days when the Republican Party had conservative Christians in its back pocket are over.

“We’re all friends, but we have come to the same place independently,” Dionne said in an interview about his contribution, “Souled Out: Reclaiming Faith and Politics After the Religious Right.”

The book tells the recent history of religion’s role in American politics and the outlook for the future.

Dionne describes the 2004 election as the “high point of polarization around issues related to religion and culture.” In the vein of presidential hopeful Sen. Barack Obama (D-Ill.), Dionne describes an America that is not as divided — especially on the key issue of abortion — as recent religious rhetoric might suggest.

“Young people are more culturally moderate than they used to be,” Dionne said. “A lot of people who are pro-choice are willing to sit down with their pro-life brothers and sisters and say, ‘OK, we can’t agree on whether abortion should be legal, but we can agree that the rate of abortion is much too high.’

“We’re at the beginning of that conversation now, and that’s very positive. It at least partially reduces the polarization around abortion.”

Dionne — a Washington Post columnist, Brookings Institution fellow and Georgetown University professor — said he has written so many columns on religion during his career (which also included a stint covering the Vatican for The New York Times in the 1980s) that it seemed natural for him to write a book on the topic.

Religion and politics “have been a personal obsession or concern of mine my whole life,” Dionne said. “I grew up in one of those households where we violated the rule that the two things you couldn’t talk about were religion and politics. We talked about those things all the time.”

Although Dionne wrote “Souled Out” before the 2008 presidential contest began in earnest, he argues that the Democratic field is paradoxically more overtly Christian than the Republican side.

He notes a 2006 speech in which Obama needled both Republicans he accused of wanting to impose their theology on the country and Democrats who bristle at any mention of religion.

“That was one of the best speeches on this subject in many, many years,” Dionne said. “He spoke to people across the board, including some very conservative religious people.”

Dionne also points to a general trend of increasing moderation of religious people in America. Christians who support abortion rights are acknowledging the horror of the practice, he writes, and Christians who used to vote exclusively on abortion are looking at other issues, too, including poverty and the AIDS crisis in Africa.

That increases the number of voters up for grabs and points to a political chess match that should make the next few elections interesting, Dionne said.

“If the Democratic Party could up its percentage of the white evangelical vote to 25 or 30 percent, our politics would be transformed,” he said. “It would be the equivalent of the Republican Party upping its share of the African-American vote to 20 percent.

“It would be a party taking a significant portion of the opposition party’s base vote.”

America has reached a point where the phrase “Christian Democrat” is no longer an oxymoron, Dionne, Sullivan and Wallis agree.

“I became a liberal because I was a Christian,” Dionne said. “It may be an odd thing for someone to say now, but for me it’s not so odd.”