Nor does Yoest advocate for reducing abortion by increasing access to birth control. When I asked what she thought about a study, published in October, which found a 60 to 80 percent drop in the abortion rate, compared with the national average, among women in St. Louis who received free birth control for three years, she said, “I don’t want to frustrate you, but I’m not going to go there.” She referred me to a critique of the study’s methodology in National Review. “It’s really a red herring that the abortion lobby likes to bring up by conflating abortion and birth control,” she said when pressed on PBS last year. “Because that would be, frankly, carrying water for the other side to allow them to redefine the issue in that way.”

Yoest doesn’t like to speak this bluntly — she was taken aback when I reminded her of the PBS quote. And she is careful to avoid missteps like the Missouri Senate candidate Todd Akin’s comment in August that victims of “legitimate rape” don’t need access to abortion because they don’t become pregnant, or the claim at the end of October by Richard Mourdock, the Indiana Senate candidate, that when women do become pregnant from rape, “that is something God intended to happen.”

In the aftermath of Akin’s statement, The St. Louis Post-Dispatch reported on a 1972 essay by an obstetrician named Fred Mecklenburg, who cited a Nazi experiment in which women were told they were on their way to die in the gas chambers — and then were allowed to live, so that doctors could check whether they would still ovulate. Since few did, Mecklenburg claimed that women exposed to the emotional trauma of rape wouldn’t be able to become pregnant, either. (He also argued that rapists are infertile because they masturbate a lot.) The essay was published in a book financed by A.U.L. When I asked Yoest about this, she tried to bat away the connection, stressing that he was also a member of the American Association of Planned Parenthood Physicians. “I just think you’re going back decades and decades,” she told me. When I asked what she thought about Akin’s reliance on bogus science, she said, “I’m not going to answer that.” Though Yoest agrees with Akin that abortion should be illegal in every circumstance, she said that talking about “the minutiae of the rape exception is not where it’s at at all.” It was as if Akin had undone all her careful framing. “It’s a distraction. It’s not relevant to the discussion.”

It’s hard to remember now, but for a brief moment around the time the Supreme Court decided Roe in 1973, it looked as if legalizing abortion would not be hugely divisive. Between 1967 and 1970, 17 states, including Alaska, Arkansas, Georgia, Kansas, North Carolina, South Carolina and Virginia, lifted some restrictions on the procedure. The vote for Roe on the Supreme Court was 7 to 2, with conservative Republican appointees signing on. In a Gallup poll, 68 percent of Republicans and 59 percent of Democrats said in 1972 — the year after A.U.L. was founded — that the decision to abort should be solely between a woman and her doctor.

As those polls indicate, opposing abortion wasn’t always a moral imperative for the Republican Party. But it would soon become a tactical one. In 1979, two G.O.P. strategists, Richard Viguerie and Paul Weyrich, seized on the issue as a tool for wooing Catholic and evangelical voters to the party. As Linda Greenhouse and Reva B. Siegel write in their book, “Before Roe v. Wade,” the pair approached the Rev. Jerry Falwell with the idea of organizing a socially conservative “Moral Majority,” with abortion as the central issue. Vigurie and Weyrich also set up an early anti-abortion political action committee for the 1980 election, which they used to help get like-minded candidates elected. And in fact, around that time Republicans in Congress started voting for abortion restrictions at a higher rate than Democrats — even though Republican voters would remain more likely to be pro-choice than Democrats until the late 1980s.

As the issue heated up, anti-abortion groups, including A.U.L., began to put more muscle into fighting for restrictions on the state level — chipping away at Roe one legislature at a time rather than focusing all their efforts in D.C. Early state bills mandated waiting periods and parental consent for minors, restrictions that still poll well today. By this time, however, the movement had attracted its share of zealots, and this faction derided these laws as half-measures and took more direct action — chaining themselves to clinics and, in the most extreme cases, bombing them.