EVER since 1973, when the Supreme Court ruled that women have a limited constitutional right to end their pregnancies, states have imposed restrictions designed to curtail that right or make it more difficult to exercise. Two recent examples illustrate the varying levels of intensity with which pro-life activists are trying to chip away at Roe v Wade. Last week in Oklahoma, lawmakers passed a bill that undermines the very basis of Roe. By a vote of 33-12 in the Senate and 59-9 in the House of Representatives, Senate Bill 1552—which would have made it a felony for doctors to perform abortion unless the procedure is necessary to save the woman’s life—sailed through the Oklahoma legislature. But the governor, who is pro-life, Mary Fallin, vetoed the bill on the grounds that it was clearly unconstitutional. “The bill is so ambiguous and so vague”, she wrote, “that doctors cannot be certain what medical circumstances would be considered ‘necessary to preserve the life of the mother.’” So while she “continue[s] to support a re-examination of the United States Supreme Court’s decision in Roe v Wade, this legislation cannot accomplish that re-examination”. A more “direct path to a re-examination” of Roe “is the appointment of a conservative, pro-life justice to the United States Supreme Court”.

Most states have used a slightly more subtle strategy to undermine abortion rights. On May 25th, South Carolina became the 17th state to ban abortion at the 20th week of pregnancy when Governor Nikki Haley signed House Bill 3114, the Pain-Capable Unborn Child Protection Act, into law. The legislation is based on the highly disputed claim that a fetus begins to feel pain halfway through pregnancy; in 2005, the Journal of the American Medical Association published a study finding that fetal awareness of pain “probably does not exist before 29 or 30 weeks”. The ban permits few exceptions: even standard loopholes for rape and incest are not available. Doctors may only perform abortions after 19 weeks if the fetus has an abnormality that would cause it to die outside the womb or if the procedure is necessary “to avert [the] death” of the pregnant woman or to prevent “substantial and irreversible physical impairment of a major bodily function”. The latter exception, the bill’s authors were careful to note, does not include “psychological or emotional conditions”.

The South Carolina law is decidedly less sweeping than the ill-fated blanket ban in Oklahoma, but it still faces constitutional hurdles. First is the problem entangling three similar laws (in Arizona, Georgia and Idaho) in state and federal courts: it bans abortion too early in pregnancy. Roe set the advent of the third trimester (about 28 weeks) as the point at which a state’s interest in protecting fetal life becomes “compelling” and states may regulate abortion. Two decades later in Planned Parenthood v Casey, the Supreme Court abandoned the trimester framework and set fetal viability (the ability of a fetus to survive outside the womb) as the new point when states could ban abortion. That threshold is earlier than 28 weeks—today, given the state of medical technology, it stands at about 23 or 24 weeks.

Interestingly, 20-week state bans count pregnancy as beginning at the point of fertilisastion—about two weeks after the conventional understanding of the beginning of pregnancy, which is the date the woman’s last menstrual period began. So on the typical pregnancy calendar, House Bill 3114 bans abortion beginning at week 22, which makes the law is just slightly off the constitutional track. But just as it makes little sense to say that a woman is a little bit pregnant, it is no saving grace to say that a law is only slightly unconstitutional.

And there is another significant problem with the law: its failure to include an exception permitting abortion when it is necessary to protect the woman’s health. Roe and its progeny all demand that any regulation on abortion contain a rider allowing doctors to perform abortions when the life or health of the woman is at stake. By striking “health” from that proviso—and effectively saying that a woman must carry a fetus to term if it endangers her well-being, unless it threatens it gravely—South Carolina law runs afoul of settled Supreme Court abortion-rights law. The justices have not weighed in on any of the 20-week bans—and given their 8-member bench and ideological balance of power, are unlikely to agree to anytime soon—but eventually the Supreme Court will have to resolve whether mounting state efforts to abort Roe have gone too far.