Without knowing this history, Williams argues, it’s difficult to understand why pro-life views have had such staying power in American politics, even as public opinion on other social issues, such as LGBT rights and birth-control use, has steadily shifted to become more permissive. Abortion, he says, has a different history. Its early opponents thought it was their duty, and their government’s duty, to protect the unborn alongside the poor and the weak. They believed their position offered women empowerment, not oppression.

Most importantly, this history shows how contorted the abortion debate has become, as women’s bodies and children’s futures have been turned into rhetorical proving grounds for politicians left and right. Today, pro-life Democrats are nearly extinct, and openly pro-choice Republicans rarely make it to a national stage like this year’s presidential race. Fifty years ago, this wasn’t the case. What happened to America’s progressive pro-lifers?

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If the first advocates of abortion legalization in America were doctors, their most vocal opponents were their Catholic colleagues. By the late 19th century, nearly all states had outlawed abortion, except in cases in which the mother’s life was threatened. As Williams writes, “The nation’s newspapers took it for granted that abortion was a dangerous, immoral activity, and that those who performed abortions were criminals.” But in the 1930s, a few doctors began calling for less harsh abortion bans—mostly “liberal or secular Jews who believed that Catholic attempts to use public law to enforce the Church’s own standards of sexuality morality violated people’s personal freedom,” according to Williams. In 1937, the National Federation of Catholic Physicians’ Guilds issued a statement condemning these abortion supporters, who, they said, would “make the medical practitioner the grave-digger of the nation.” Although some Protestants had been involved in early efforts to prohibit early-term abortions, in these early years, resistance was overwhelmingly led by Catholics.

Some hospitals interpreted abortion laws loosely, relying on psychiatrists to certify that a woman might be at risk of suicide if she were forced to carry her pregnancy to term. But even some of the doctors who performed these procedures and advocated abortion-law liberalization—like Alan Guttmacher, a New York gynecologist who went on to head Planned Parenthood in the 1960s and is the namesake of one of today’s most prominent pro-choice advocacy organizations—shrunk from full-on support of the procedure, hoping that birth control would eliminate its need. “I don’t like killing,” Guttmacher said, but he believed abortion was justified if it preserved a mother’s life.

Meanwhile, a handful of courts were taking on a different aspect of the debate: whether abortion was a violation of human rights. From 1939 to 1958, five state supreme courts and the U.S. District Court in D.C. handed down rulings that recognized fetal personhood. These rulings lined up with the convictions of theologically conservative Catholics, who believed that life begins at conception, and this group may very well have influenced the decisions. As Guttmacher wrote in 1963, “The Catholic Church is so well mobilized and makes up such a large percentage of the population that changing the law of any state in the Northeast of the U.S.A. is a virtual impossibility at least for the next several decades.”