Activists on both the left and the right tend to forget this irony of the First Amendment: it has been as much a weapon of religious oppression as a safeguard for liberty. In the 19th and early 20th century, when public school teachers read from a Protestant translation of the Bible in class, many Americans saw benign reinforcement of American values. If Catholic parents complained, officials told them that their Roman dogma was their own private concern. The underlying logic here was not religious neutrality.

The Protestant bias of the American public sphere has mellowed over time, but it still depends on “Christian secularism,” said Elizabeth Shakman Hurd, a political scientist at Northwestern University. This is a “political stance” premised on a “chiefly Protestant notion of religion understood as private assent to a set of propositional beliefs,” she told me. Other traditions, such as Judaism and Islam and to some degree Catholicism, do not frame faith in such rationalist terms, or accept the same distinction between internal conviction and public argument. The very idea that it is possible to cordon off personal religious beliefs from a secular town square depends on Protestant assumptions about what counts as “religion,” even if we now mask these sectarian foundations with labels like “Judeo-Christian.”

Conservative Christian activists hold those sectarian foundations more dearly than they admit, and they are challenging the Obama administration’s efforts to frame access to contraception and same-sex marriage as civil rights immune to the veto of “private” conscience. Alan Sears, president of the legal advocacy organization Alliance Defending Freedom, sees an unprecedented threat to religious liberty in the harsh fines facing employers who refuse to cover contraception in their insurance programs. “It is a death penalty. It is a radical change,” he told me. “It’s one thing when you’re debating about public space, but it’s another when you say, if you don’t surrender your conscience, you’re out of business.”