Avoiding church does not excuse Americans from marking the birth of Jesus, however. Most of us have no choice but to stay home from work or school — and if you complain about this glaring exception to the separation between church and state, you must be a scrooge with no heart for tradition. Christmas has been a federal holiday for 142 years.

Yet Christianity’s preferential place in our culture and civil law came under fire this year, and not simply because more Americans reject institutional religion. The Obama administration subtly worked to expand the scope of protected civil rights to include access to legal marriage and birth control. Catholic bishops and evangelical activists declared that Washington was running roughshod over religious liberty and abandoning the country’s founding values, while their opponents accused them of imposing one set of religious prejudices on an increasingly pluralistic population. The Christian consensus that long governed our public square is disintegrating. American secularism is at a crossroads.

The narrative on the right is this: Once upon a time, Americans honored the Lord, and he commissioned their nation to welcome all faiths while commanding them to uphold Christian values. But in recent decades, the Supreme Court ruled against prayer in public schools, and legalized abortion, while politicians declared “war on Christmas” and kowtowed to the “homosexual lobby.” Conservative activists insist that they protest these developments not to defend special privileges for Christianity, but to respect the founders’ desire for universal religious liberty — rooted, they say, in the Christian tradition.

The controversial activist David Barton has devoted his career to popularizing this “forgotten history” through lectures, books and home-school curriculums. Mr. Barton insists that “biblical Christianity in America produced many of the cherished traditions still enjoyed today,” including “protection for religious toleration and the rights of conscience.”

Bryan Fischer, spokesman for the American Family Association, told me that he saw the “nones” as proof that “the foundations of our culture are crumbling.” The Pew poll, he said, “is one of the signs.” A couple of weeks after we spoke, he told a radio audience that God did not protect the children killed in the Newtown, Conn., massacre because of the Supreme Court decisions banning prayer and Bible reading in public schools. “God is not going to go where he is not wanted,” Mr. Fischer said.

How accurate is this story of decline into godlessness? Is America, supposedly God’s last bastion in the Western world, rejecting faith and endangering religious liberty?