Almost all Americans will celebrate Christmas in some capacity this year, but why they are celebrating increasingly has less to do with the birth of Jesus as fewer Americans believe in the biblical Christmas story and a growing number are opting not to attend church services.

According to a new report from the Pew Research Center, about half of all Americans (51 percent) plan to celebrate Christmas in church, down three percentage points from 2013. And that trend appears likely to continue in coming years: Just four in 10 millennials plan to attend church this Christmas, compared to six in 10 baby boomers. And when it comes to whether Christmas is “religious” or “cultural,” just 32 percent of millennials said it is more religious, 20 points behind boomers.

Fewer Americans believe in the biblical Christmas story and a growing number are opting not to attend church services.

And those fights for parking at Midnight Mass could become less fraught this year, with just 68 percent of U.S. Catholics planning to attend church this Christmas, down 8 percentage points in just four years.

The Pew report also asked Americans about their thoughts on four elements of the traditional Christmas story: that Jesus was born to a virgin, that he was laid in a manger, that an angel announced his birth to a group of shepherds and that three wise men followed a star to pay homage to the newborn.

Belief in these elements is dropping among all Americans, including among self-described Christians.

Nearly six in 10 Americans believe all four aspects of the traditional Christmas narrative, down from 65 percent in 2014. Among Catholics, 71 percent believe all four, down five points from 2014. (The most widely believed aspect is that Jesus was laid in a manger, with 75 percent of Americans saying they believe this, while just 66 percent of Americans believe Jesus was born to a virgin. Belief in each of these aspects dropped more than 5 percentage points since 2014.)

Then there is the so-called War on Christmas, a media campaign started by the Catholic League and championed by former Fox News personality Bill O’Reilly, who each December highlighted the grievances some Christians felt during the holiday season. Mr. O’Reilly departed Fox in April following revelations of sexual harassment, long before his annual War on Christmas monologues would begin.

But the theme was picked up by President Donald Trump, who as a candidate pledged that retailers would say “Merry Christmas” should he be elected. In an October speech, Mr. Trump declared victory, telling an audience of evangelical Christians, “We’re saying Merry Christmas again.”

Turns out, most Americans do not seem to care.

According to Pew, 52 percent of Americans have no preference about how they are greeted in stores during the holiday season. In 2005, 43 percent of Americans said they prefered to hear “Merry Christmas,” but today that number is just 32 percent.

But, like seemingly everything else in the United States today, one’s holiday greeting preference appears tied to party loyalty. More than half of Republicans (54 percent) say they prefer to hear “Merry Christmas” in stores, while 61 percent of Democrats say it does not matter to them.

And when it comes to expressions of the Christmas story on public land, most Americans agree that items such as Nativity scenes are O.K., especially if paired with other holiday symbols, including Hanukkah displays.

The results were released on Dec. 12 by Pew and are based on telephone interviews conducted from Nov. 29 to Dec. 4 with 1,503 adults.

Michael J. O’Loughlin is the executive editor and C.E.O. of National Catholic Reporter. Previously he was the national correspondent at America. He is also the author of Hidden Mercy: AIDS, Catholics, and the Untold Stories of Compassion in the Face of Fear.