The country has grown less religious since the 1970s, while frequent churchgoers now are much more likely to vote Republican or support the Tea Party, according to recent studies.
The rise of megachurches, with their memberships in the thousands, also fuels the misperception that most Americans attend services weekly, when only one in four Americans actually do, he added.
"The Michele Bachmanns and Rick Perrys of the world are playing to a base that's much smaller than it was in the 1970s and 1980s," said Chaves, whose new book, American Religion: Contemporary Trends, analyzes trends based on data from the General Social Survey and the National Congregations Study.
Using data collected between 1972 and 2008, Chaves said, America not only is losing its religion, but also has lost confidence in religious leaders and wants them to be less involved in politics.
Researchers say the trends reflect myriad factors—disillusionment with clergy and political scandals; the country's increasing diversity, fueled by immigration and intermarriage; and younger generations that tend to be more highly educated and socially liberal.
Chaves also interprets these trends as a "backlash" against the politicization of religion that began with Jerry Falwell and the rise of the Religious Right in the 1970s.
The Tea Party's sinking approval rating—currently at 20 percent, below Republicans, Democrats, atheists and Muslims—signals a growing discomfort with mingling faith and politics, including the kind of "overt religious language and imagery" sometimes used on the campaign trail, Putnam and Campbell recently wrote in The New York Times.
What's more, Putnam and Campbell say, the Tea Party is much more religious than originally thought. "The Tea Party's generals may say their overriding concern is a smaller government," they concluded, "but not their rank and file, who are more concerned about putting God in government."
Among the other findings in American Religion:
• There is a declining (though still very high) belief in God or a higher power: In the 1950s, 99 percent of Americans said they believed in God; in 2008, about 93 percent did.
• Nearly 20 percent of Americans now say they have no religion, compared to just 3 percent in 1957.
• Only 25 percent of Americans attend weekly religious services, although up to 40 percent claim they do.
• Fewer Americans approve of their religious leaders getting involved in politics. In 1991, about 30 percent of Americans strongly agreed religious leaders should avoid political involvement; by 2008, 44 percent felt that way.
• Belief that the Bible should be taken literally dropped from about 40 percent in the early 1970s to about 30 percent in 2008; Chaves said this trend corresponds with the rise in college education.
From 1972 to 2008, the percentage of people with great confidence in religious leaders declined from 35 percent to less than 25 percent. A sharp dip around 2002 was probably due to the Catholic Church clergy abuse scandal, but otherwise the trend consistently has been downward for decades, along with interest in joining the clergy.
Immigration from Africa and Asia, intermarriage and assimilation have diversified America's religious beliefs since the early 1970s.
Continuing that trend, Chaves believes Americans will grow more accepting of Muslims over the next generation, as has happened with other minorities.
He cited Putnam and Campbell's "Aunt Susan Principle," the idea that people are less suspicious of other faiths when someone they know is a member.