(RNS) Politicians often cite American “exceptionalism” and the country's high level of religiosity when boasting about one nation under God.

But this country isn’t so unique on the faith front any more, say two sociology professors.

Their new study shows Americans steadily sliding toward secular Europe with increasingly fuzzy -- or fading -- ties to church, God and religious denominations.

These changes are generational, long term and unlikely to reverse course, say Mark Chaves of Duke University and David Voas of University College London, in the latest American Journal of Sociology.

You don’t have to be an academic to notice.

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“You see it everywhere, even in the electoral politics where it is no longer essential for a presidential candidate to be religious,” said Voas, pointing to Donald Trump, who strikes many as what might be called a nominal Christian, and Bernie Sanders, a secular Jew.

Or you can look around at your friends and family. Everyone knows someone who is not religious and not shy any more about saying so, observed Chaves.

Their study addressed the debate among social scientists on the relationship between modernization and secularization.

Some argue, pointing to Europe, that the more developed a nation, the less religious its people. Other experts cite America as the exception because of its high rates of belief in God, church attendance and religious identification.

That’s no longer so, Chaves and Voas claim.

In discussing their findings, Chaves pointed to the rise of the “nones” – people who say they have no religious identity – from a barely noticed fraction in the 1950s to 21 percent of Americans in the 2014 General Social Survey conducted by the National Opinion Research Center at the University of Chicago.

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“A society in which the least religious people still claim a religious identity is importantly different from a society in which such people admit to themselves, and even tell others, that they in fact have no religion,” Chaves and Voas write.

A summary released by Duke University highlights key findings:

94 percent of Americans born before 1935 claim a religious affiliation. For the generation born after 1975, that number drops to 71 percent.

68 percent of Americans 65 and older said they had no doubt God exists, according to the study. But just 45 percent of young adults, ages 18-30, had the same belief.

41 percent of people 70 and older said they attend church services at least once a month, compared to just 18 percent of people 60 and younger.

And the study reports the number of people who never attend religious services has doubled in two and a half decades: It was 26 percent in 2014, up from 13 percent in 1990.

While other Western nations are even less religious than the U.S., the patterns are very much alike. Chaves and Voas did 10 charts detailing shifts in belief in God, worship attendance and religious identification for the U.S., England, Australia, New Zealand and Europe as a whole.

READ: ANALYSIS: 7.5 million Americans lost their religion since 2012

“No matter which one you look at, they all look the same -- the trends are heading the same direction” toward secularization,” said Chaves.

"The evidence for a decades-long decline in American religiosity is now incontrovertible. Like the evidence for global warming, it comes from multiple sources, shows up in several dimensions, and paints a consistent factual picture,” the study says.

The authors do not speculate as to whether there’s a cause-and-effect relationship between modernization and declining religious attachment. But, said Chaves, “We are not as exceptional as we once thought.”

(Cathy Lynn Grossman is senior national correspondent for RNS)