The decline was fueled mostly by losses among Roman Catholics and mainline Protestants. However, even in parts of the Bible Belt, conservative Christians who hadn't been very active in church are now feeling more comfortable saying they're no longer religious. The membership ranks of some evangelical denominations, such as the Southern Baptist Convention, are shrinking.

At the same time, the segment of Americans who say they have no particular religion has increased from 16 percent to 23 percent, Pew found. That's close to the share of evangelicals, who comprise just over 25 percent of the population.

At the same time, evangelicals are wrestling with being on the losing side of the fight over same-sex marriage. It was not only a defeat on a deeply significant religious and moral issue, but also evidence of a lack of conservative Christian influence over public opinion. More than half of Americans now support same-sex marriage.

Politically, white evangelicals remain one of the most important blocs in the Republican Party, and they continue to shape the early presidential primaries. But with the diminishment of old-guard religious right groups, Christian conservatives no longer have a unifying leader. As a result, evangelicals are splintering, diluting their influence. And they can't match the growth rate of groups who tend to support Democrats: Latinos, young people and people who are unaffiliated with a religion.

WHY ARE CONSERVATIVE CHRISTIANS SO ANXIOUS?

Evangelicals are deeply worried about the fallout from the spread of LGBT rights and the growth of secularism.

They point to cases like the fines levied on a New Mexico photographer and Oregon baker for refusing business related to gay weddings. Conservative Christians fear their schools and colleges could lose their tax-exempt status or accreditation over codes of conduct barring same-sex relationships.

A 1983 U.S. Supreme Court ruling allowed the IRS to revoke tax-exempt status from religious schools that banned interracial dating. In the Supreme Court gay marriage case last year, U.S. Solicitor General Donald Verrilli, representing the government, was asked whether something similar could happen to Christian schools, which often provide housing for married students. "It's certainly going to be an issue," he responded, causing alarm in the evangelical blogosphere.

And religious conservatives worry about new rules added to government contracts that will affect faith-based social service agencies. For example, Catholic Charities in Illinois shuttered its adoption program over a new state rule that agencies with taxpayer funding can't refuse placements with same-sex couples.

Gay rights groups consider these changes a welcome corrective to decades of discrimination. They contend conservatives are using conscience rights and religious freedom complaints as an end run around advances for LGBT people. But conservative Christians say they are just seeking a balance between religious liberty and civil rights.

HOW ARE EVANGELICALS REACTING?

Evangelicals are debating whether they should even more fiercely wage the culture war, withdraw back into their own communities or stay engaged with Americans of other views, not only to help shape public discussion of morality but also to try and bring people into the church.

Christian publishers are churning out books and Bible studies on this last strategy, such as "Onward," by Russell Moore, "Thriving in Babylon," by Larry Osborne, and "Good Faith, Being a Christian When Society Thinks You're Irrelevant or Extreme," by Gabe Lyons and David Kinnaman.

Advocates of this strategy generally feel the sharp rhetoric of the religious right -- on homosexuality and other issues -- ultimately hurt Christians. This group aims to confidently advocate for their beliefs, no matter how unpopular, but without vilifying their opponents. These evangelicals are also emphasizing issues that can cross ideological lines, including fighting racism and human trafficking, as part of highlighting the more compassionate side of their faith.

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