Yesterday, Republican Ohio Gov. John Kasich vetoed the so-called “heartbeat bill,” a measure that would have banned all abortions after about six weeks of pregnancy, or before many women even know that they are pregnant. At the same time, Kasich signed a bill banning abortion after 20 weeks of pregnancy, with exceptions only for saving a pregnant woman’s life or preventing the “substantial and irreversible impairment of a major bodily function.”

While Kasich’s decision to sign the 20-week ban while vetoing the six-week ban may make him seem like a relative moderate on abortion rights, he is anything but. In fact, the 20-week ban that Kasich did sign is a much bigger threat to legal abortion than was the “heartbeat bill” that he vetoed. This is because while the “heartbeat bill” would almost certainly have been struck down in the courts as unconstitutional, the 20-week ban is part of a careful strategy by anti-choice groups to strike at the heart of Roe v. Wade.

The anti-choice movement, with the leadership of Americans United for Life and the National Right to Life Committee, has worked to push through 20-week abortion bans in states around the country. Shortly before this year’s election, Donald Trump attempted to consolidate his support from the anti-abortion movement in part by promising to sign a federal version of the bill.

(Although these bills are generally referred to as 20-week bans, many, like Ohio’s, actually ban abortion after about 22 weeks as determined by the medically accepted protocol for measuring the length of a pregnancy. Abortions after 20 weeks of pregnancy are very rare, making up only about 1 percent of all procedures in the U.S.)

Abortion rights opponents market these bills as “pain-capable” or “fetal pain” bills, claiming—with inconclusive scientific evidence—that they ban abortion at the point at which a fetus can feel pain. But their real purpose is to launch a calculated attack at Roe, which largely protects the right to abortion up to the point of viability, which generally occurs at about 24 weeks of pregnancy, although recent medical advances have allowed a small number of children born even earlier to survive.

By pushing through legal abortion limits that kick in at just before the point where most fetuses would be viable outside the womb, the anti-choice movement is attempting to kick down a central pillar of Roe with the hope that the decision’s larger protections of legal abortion will come down with it. As Americans United for Life’s Ovide Lamontagne told Talking Points Memo last year, “We do think these kinds of cases and these kind of laws will ultimately lead to the erosion and outright reversal of Roe v. Wade. This is the kind of law that could lead the court to say, ‘It is time for us to get out of this business.'”

There is a reason that mainstream anti-choice groups have gotten behind 20-week abortion bans while shying away from more extreme measures like the “heartbeat bill.” An outright attack on Roe via a six-week abortion ban would be extremely unlikely to survive any court challenge as long as Roe survives; 20-week bans are carefully calculated to prevent Roe from surviving at all.

In Ohio, the “heartbeat bill” was particularly suited to making all other anti-choice legislation seem reasonable by comparison. It’s chief champion, Janet Porter, is an extremist Religious Right activist who has, for instance, blamed Noah’s Flood on gay marriage.

In a press release responding to the veto, Porter lambasted Kasich for his “betrayal” and declared that his “political career is over.” But in reality, Kasich’s move was perfectly designed to preserve his image as a Republican moderate while inflicting the maximum possible damage on Roe v. Wade.