By David Lauter, Tribune Washington Bureau (TNS)

WASHINGTON — The U.S. has become significantly less Christian in the last eight years as the share of American adults who espouse no systematic religious belief increased sharply, a major new study found.

For what is likely the first time in U.S. history — certainly the first since the early days of the country — the actual number of American Christians has declined. Christianity, however, remains by far the nation’s dominant religious tradition, according to the new report by the nonpartisan Pew Research Center.

The rapid increase in the number of adults without ties to traditional religious institutions has strong implications for other social institutions and for politics.

Whether a person attends religious services regularly is among the strongest predictors of how he or she will vote, with traditional religion strongly tied to the Republican Party, at least among white Americans.

The decline in traditional religious belief adds to the demographic challenges facing the GOP, which already faces difficulties because of its reliance on white voters in a country that has grown more racially diverse.

The interaction between religion and politics may work both ways. Some scholars believe that close ties between traditional religion and conservatism, particularly on issues such as same-sex marriage, have led many younger Americans to cut their ties with organized religion.

Almost one in five American adults were raised in a religious tradition but are now unaffiliated, the study found. By contrast, only four percent have moved in the other direction.

Because the U.S. census does not ask questions about religion, the massive religion surveys by the Pew Research Center have become a chief source of information on the U.S. religious landscape.

The current survey questioned 35,071 U.S. adults last summer. Its huge size allows detailed analysis of even fairly small religious groups. The margin of error for the full sample is plus or minus six-tenths of a percentage point.

The U.S. still remains far more religious than most other economically advanced countries, but the significant increase in the share of Americans who do not follow a traditional religious belief mirrors trends in Europe and elsewhere.

Just short of one in four Americans now describe themselves as being agnostic, atheist, or simply “nothing in particular,” up from roughly one in six in 2007, according to the new study. The ranks of the “nones,” as the study labels them, have grown in large part from people abandoning the religion in which they were raised.

By contrast, Christian ranks have eroded. Roughly 173 million adult Americans identify as Christian, just under 71 percent of the U.S. population. That’s down from 178 million, or 78 percent of the U.S., in 2007. The total U.S. adult population grew by about eight percent during that eight-year period.

Protestants, who once dominated the U.S. population, no longer form a majority, the study found. About 47 percent of the U.S. population identifies with some Protestant denomination, down from just over half in 2007.

The decline has been uneven, with mainline denominations, such as Methodists and Presbyterians, shrinking more quickly than evangelical churches.

Slightly fewer than one in six adult Americans identify with the mainline Protestant churches, according to the survey. Evangelicals, by contrast, make up about one-quarter of the adult U.S. population. They now form a majority among those who identify as Protestant.

Another seven percent of American adults identify with historically black Protestant churches, a share that has remained relatively stable.

Catholics, about one in five Americans, have also seen some decline in numbers since 2007, the study found, although some other studies have found a more recent uptick. Almost 13 percent of American adults are former Catholics — the largest single group of people who have left a faith in which they were raised.

Among non-Christian faiths, Judaism remains the largest in the U.S., although only about two percent of the U.S. population identifies as Jewish. The number is up very slightly from what the survey found in 2007.

Islam, Hinduism, and Buddhism each have less than one percent of the U.S. population, although the Muslim and Hindu population have both grown rapidly, reflecting immigration from Asia.

Photo: Mor via Flickr