Alexis de Tocqueville's 19th-century observation that "the Christian religion" had a greater influence on America than any other country in the world might still be true, but if he were visiting today, he'd find Americans dropping their formal religious affiliations in unprecedented numbers.
In the last five years, the number of people who claim no religious affiliation has increased from slightly more than 15 percent to just under 20 percent of all U.S. adults, according to a new study  by the Pew Forum on Religion & Public Life, one of seven projects that make up the Pew Research Center. The study was done in partnership with the PBS program "Religion & Ethics Newsweekly."
According to the report, titled " 'Nones' on the Rise,"  the almost 20 percent (33 million people) who are unaffiliated include 13 million self-described atheists and agnostics, or almost 6 percent of the U.S. population.
The study also established that only 48 percent of American adults say they are Protestant, the "first time in Pew Research Center surveys that the Protestant share of the population has dipped significantly below 50 percent," the report says. Five years ago, Protestants made up 53 percent of the population.
In comments Saturday to a meeting of the Religion Newswriters Association held in Bethesda, Md., the researchers said the new numbers, based both on recent surveys as well as other materials from past polling, confirms a consistent trend showing a declining attachment to religious institutions. The drop occurs across such demographic divides as age, levels of education and income.
In an interview with NCR, Pew Forum senior researcher Gregory Smith described as "twin milestones" the increase in the number of unaffiliated and the drop in the Protestant population, a decrease that occurred primarily among white Protestants among both those who describe themselves as evangelicals and those who describe themselves as non-evangelicals.
While the margins of error, a function of the size of polling samples, for various components of the study range from 2.1 to 4.5 percentage points, Smith said the margin of error for the findings regarding the number of unaffiliated and the number of Protestants is 0.9 percentage points because it is based on polling of 17,010 people, an unusually large number. He said the figure is an aggregate of polls done in a six-month period by the Pew Research Center for the People and the Press.
The finding that Protestants now make up less than half the adult population in the United States is an especially dramatic result because the country has always been mostly Protestant, Smith said. As recently as the 1980s, Protestants accounted for six in 10 Americans, he added.
Lack of affiliation, the study points out, doesn't mean a lack of religion or spirituality. According to the study, "many of the country's 46 million unaffiliated adults are religious or spiritual in some way. Two-thirds of them say they believe in God (68 percent)" and "more than a third classify themselves as 'spiritual' but not 'religious' (37 percent)." Further, 21 percent of them say they pray every day, and most of them, according to the survey, are not hostile toward organized religion but "think that churches and other religious institutions benefit society by strengthening community bonds and aiding the poor."
How long denominations will be around to provide such benefits is the question. In fact, the only religious groups to remain relatively unchanged are Black Protestant (8 percent), other minority Protestant (6 percent), Orthodox (1 percent), Mormon (2 percent) and Catholic (23 percent). The stability in the Catholic population has largely to do with the influx of Latin American immigrants, previous Pew studies have documented.
The percentage of the population identifying as Christian dropped from 78 percent in 2007 to 73 percent this year.
Among the oldest generation surveyed, termed the "Greatest" in the survey and consisting of those born between 1913 and 1927, the number of unaffiliated has dropped from 7 percent to 5 percent between 2007 and this year.
In the "Silent" generation, born 1928-1945, the percentage of unaffiliated remains unchanged at 9 percent in the same five-year period.
"Boomers," born 1946-1964, show an increase of unaffiliated over the same period, from 12 percent to 15 percent.
The number of unaffiliated among "Gen Xers," born 1965-1980, increased from 18 percent to 21 percent.
"Older Millennials," born 1981-1989, showed an increase in unaffiliated from 26 percent to 30 percent.
Finally, among "Younger Millennials," born 1990-1994 and surveyed for the first time, the percentage of unaffiliated was 34 percent.
So while the lack of affiliation increases among the young, the trend to drop religious affiliation began with the boomers and increases in subsequent generations.
The study shows the percentage of Americans raised without an affiliation has risen slowly, from about 3 percent in the early 1970s to about 8 percent during the past decade. However, the current survey found that about 74 percent of adults who are now unaffiliated were raised "with some affiliation."
If the ranks of those who claim no affiliation are growing, the number who say religion is very important in their lives has remained fairly constant -- 58 percent today compared with 61 percent in 2007. At the same time, the number who say prayer is an important part of their daily lives is at 76 percent, the same figure as 25 years ago.
And the United States remains far more religious than other countries. For instance, according to the report, the percentage of those in Britain who see religion as very important in their lives stands at 17 percent; in France, 13 percent; Germany, 21 percent; and Spain, 22 percent.
The downturn in affiliation is reflected in a downturn in church attendance. Between 2003 and 2012, the number of U.S. adults who report attending weekly or more often has dropped from 39 percent to 37 percent; the number who attend monthly or yearly dropped one point, from 34 percent to 33 percent; and the number who attend seldom or never rose from 25 percent to 29 percent.
[Tom Roberts is NCR editor at large. His email address is email@example.com.]